Test the vesa_attributes field in struct screen_info for compatibility with VGA hardware. Vesafb currently tests bit 1 in screen_info's capabilities field, It sets the framebuffer address size and is unrelated to VGA.
Section 4.4 of the Vesa VBE 2.0 specifications defines that bit 5 in the mode's attributes field signals VGA compatibility. The mode is compatible with VGA hardware if the bit is clear. In that case, the driver can access VGA state of the VBE's underlying hardware. The vesafb driver uses this feature to program the color LUT in palette modes. Without, colors might be incorrect.
The problem got introduced in commit 89ec4c238e7a ("[PATCH] vesafb: Fix incorrect logo colors in x86_64"). It incorrectly stores the mode attributes in the screen_info's capabilities field and updates vesafb accordingly. Later, commit 5e8ddcbe8692 ("Video mode probing support for the new x86 setup code") fixed the screen_info, but did not update vesafb. Color output still tends to work, because bit 1 in capabilities is usually 0.
Besides fixing the bug in vesafb, this commit introduces a helper that reads the correct bit from screen_info.
Signed-off-by: Thomas Zimmermann tzimmermann@suse.de Fixes: 5e8ddcbe8692 ("Video mode probing support for the new x86 setup code") Cc: stable@vger.kernel.org # v2.6.23+ --- drivers/video/fbdev/vesafb.c | 2 +- include/linux/screen_info.h | 5 +++++ 2 files changed, 6 insertions(+), 1 deletion(-)
diff --git a/drivers/video/fbdev/vesafb.c b/drivers/video/fbdev/vesafb.c index 8ab64ae4cad3e..5a161750a3aee 100644 --- a/drivers/video/fbdev/vesafb.c +++ b/drivers/video/fbdev/vesafb.c @@ -271,7 +271,7 @@ static int vesafb_probe(struct platform_device *dev) if (si->orig_video_isVGA != VIDEO_TYPE_VLFB) return -ENODEV;
- vga_compat = (si->capabilities & 2) ? 0 : 1; + vga_compat = !__screen_info_vbe_mode_nonvga(si); vesafb_fix.smem_start = si->lfb_base; vesafb_defined.bits_per_pixel = si->lfb_depth; if (15 == vesafb_defined.bits_per_pixel) diff --git a/include/linux/screen_info.h b/include/linux/screen_info.h index 75303c126285a..95f2a339de329 100644 --- a/include/linux/screen_info.h +++ b/include/linux/screen_info.h @@ -49,6 +49,11 @@ static inline u64 __screen_info_lfb_size(const struct screen_info *si, unsigned return lfb_size; }
+static inline bool __screen_info_vbe_mode_nonvga(const struct screen_info *si) +{ + return si->vesa_attributes & BIT(5); // VGA if _not_ set +} + static inline unsigned int __screen_info_video_type(unsigned int type) { switch (type) {
Thomas Zimmermann tzimmermann@suse.de writes:
Hello Thomas,
Test the vesa_attributes field in struct screen_info for compatibility with VGA hardware. Vesafb currently tests bit 1 in screen_info's capabilities field, It sets the framebuffer address size and is unrelated to VGA.
Section 4.4 of the Vesa VBE 2.0 specifications defines that bit 5 in the mode's attributes field signals VGA compatibility. The mode is compatible with VGA hardware if the bit is clear. In that case, the driver can access VGA state of the VBE's underlying hardware. The vesafb driver uses this feature to program the color LUT in palette modes. Without, colors might be incorrect.
The problem got introduced in commit 89ec4c238e7a ("[PATCH] vesafb: Fix incorrect logo colors in x86_64"). It incorrectly stores the mode attributes in the screen_info's capabilities field and updates vesafb accordingly. Later, commit 5e8ddcbe8692 ("Video mode probing support for the new x86 setup code") fixed the screen_info, but did not update vesafb. Color output still tends to work, because bit 1 in capabilities is usually 0.
How did you find this ?
Besides fixing the bug in vesafb, this commit introduces a helper that reads the correct bit from screen_info.
Signed-off-by: Thomas Zimmermann tzimmermann@suse.de Fixes: 5e8ddcbe8692 ("Video mode probing support for the new x86 setup code") Cc: stable@vger.kernel.org # v2.6.23+
The patch looks correct to me after your explanation in the commit message and looking at the mentioned commits.
Reviewed-by: Javier Martinez Canillas javierm@redhat.com
Hi Javier
Am 13.06.24 um 11:35 schrieb Javier Martinez Canillas:
Thomas Zimmermann tzimmermann@suse.de writes:
Hello Thomas,
Test the vesa_attributes field in struct screen_info for compatibility with VGA hardware. Vesafb currently tests bit 1 in screen_info's capabilities field, It sets the framebuffer address size and is unrelated to VGA.
Section 4.4 of the Vesa VBE 2.0 specifications defines that bit 5 in the mode's attributes field signals VGA compatibility. The mode is compatible with VGA hardware if the bit is clear. In that case, the driver can access VGA state of the VBE's underlying hardware. The vesafb driver uses this feature to program the color LUT in palette modes. Without, colors might be incorrect.
The problem got introduced in commit 89ec4c238e7a ("[PATCH] vesafb: Fix incorrect logo colors in x86_64"). It incorrectly stores the mode attributes in the screen_info's capabilities field and updates vesafb accordingly. Later, commit 5e8ddcbe8692 ("Video mode probing support for the new x86 setup code") fixed the screen_info, but did not update vesafb. Color output still tends to work, because bit 1 in capabilities is usually 0.
How did you find this ?
I was reading through vesafb and found that [1] and [2] look surprisingly similar, which makes no sense. So I started looking where bit 1 came from. The flag signals a 64-bit framebuffer address for EFI (see VIDEO_CAPABILITY_64BIT_BASE https://elixir.bootlin.com/linux/latest/C/ident/VIDEO_CAPABILITY_64BIT_BASE). But old VESA framebuffers are usually located within the first 32-bit range. So the bit is mostly 0 and vesafb works as expected.
[1] https://elixir.bootlin.com/linux/latest/source/drivers/video/fbdev/vesafb.c#... [2] https://elixir.bootlin.com/linux/latest/source/include/linux/screen_info.h#L...
Besides fixing the bug in vesafb, this commit introduces a helper that reads the correct bit from screen_info.
Signed-off-by: Thomas Zimmermann tzimmermann@suse.de Fixes: 5e8ddcbe8692 ("Video mode probing support for the new x86 setup code") Cc: stable@vger.kernel.org # v2.6.23+
The patch looks correct to me after your explanation in the commit message and looking at the mentioned commits.
Reviewed-by: Javier Martinez Canillas javierm@redhat.com
Thanks a lot.
Best regards Thomas
Thomas Zimmermann tzimmermann@suse.de writes:
Hi Javier
Am 13.06.24 um 11:35 schrieb Javier Martinez Canillas:
Thomas Zimmermann tzimmermann@suse.de writes:
Hello Thomas,
Test the vesa_attributes field in struct screen_info for compatibility with VGA hardware. Vesafb currently tests bit 1 in screen_info's capabilities field, It sets the framebuffer address size and is unrelated to VGA.
Section 4.4 of the Vesa VBE 2.0 specifications defines that bit 5 in the mode's attributes field signals VGA compatibility. The mode is compatible with VGA hardware if the bit is clear. In that case, the driver can access VGA state of the VBE's underlying hardware. The vesafb driver uses this feature to program the color LUT in palette modes. Without, colors might be incorrect.
The problem got introduced in commit 89ec4c238e7a ("[PATCH] vesafb: Fix incorrect logo colors in x86_64"). It incorrectly stores the mode attributes in the screen_info's capabilities field and updates vesafb accordingly. Later, commit 5e8ddcbe8692 ("Video mode probing support for the new x86 setup code") fixed the screen_info, but did not update vesafb. Color output still tends to work, because bit 1 in capabilities is usually 0.
How did you find this ?
I was reading through vesafb and found that [1] and [2] look surprisingly similar, which makes no sense. So I started looking where bit 1 came from. The flag signals a 64-bit framebuffer address for EFI (see VIDEO_CAPABILITY_64BIT_BASE https://elixir.bootlin.com/linux/latest/C/ident/VIDEO_CAPABILITY_64BIT_BASE). But old VESA framebuffers are usually located within the first 32-bit range. So the bit is mostly 0 and vesafb works as expected.
[1] https://elixir.bootlin.com/linux/latest/source/drivers/video/fbdev/vesafb.c#... [2] https://elixir.bootlin.com/linux/latest/source/include/linux/screen_info.h#L...
I see. Thanks a lot for the explanation and references.
On 6/13/24 11:02, Thomas Zimmermann wrote:
Test the vesa_attributes field in struct screen_info for compatibility with VGA hardware. Vesafb currently tests bit 1 in screen_info's capabilities field, It sets the framebuffer address size and is unrelated to VGA.
Section 4.4 of the Vesa VBE 2.0 specifications defines that bit 5 in the mode's attributes field signals VGA compatibility. The mode is compatible with VGA hardware if the bit is clear. In that case, the driver can access VGA state of the VBE's underlying hardware. The vesafb driver uses this feature to program the color LUT in palette modes. Without, colors might be incorrect.
The problem got introduced in commit 89ec4c238e7a ("[PATCH] vesafb: Fix incorrect logo colors in x86_64"). It incorrectly stores the mode attributes in the screen_info's capabilities field and updates vesafb accordingly. Later, commit 5e8ddcbe8692 ("Video mode probing support for the new x86 setup code") fixed the screen_info, but did not update vesafb. Color output still tends to work, because bit 1 in capabilities is usually 0.
Besides fixing the bug in vesafb, this commit introduces a helper that reads the correct bit from screen_info.
Nice catch, Thomas!
But do we really need this additional helper?
Signed-off-by: Thomas Zimmermann tzimmermann@suse.de Fixes: 5e8ddcbe8692 ("Video mode probing support for the new x86 setup code") Cc: stable@vger.kernel.org # v2.6.23+
drivers/video/fbdev/vesafb.c | 2 +- include/linux/screen_info.h | 5 +++++ 2 files changed, 6 insertions(+), 1 deletion(-)
diff --git a/drivers/video/fbdev/vesafb.c b/drivers/video/fbdev/vesafb.c index 8ab64ae4cad3e..5a161750a3aee 100644 --- a/drivers/video/fbdev/vesafb.c +++ b/drivers/video/fbdev/vesafb.c @@ -271,7 +271,7 @@ static int vesafb_probe(struct platform_device *dev) if (si->orig_video_isVGA != VIDEO_TYPE_VLFB) return -ENODEV;
- vga_compat = (si->capabilities & 2) ? 0 : 1;
- vga_compat = !__screen_info_vbe_mode_nonvga(si);
Instead maybe just this: ? + /* mode is VGA-compatible if BIT 5 is _NOT_ set */ + vga_compat = (si->vesa_attributes & BIT(5)) == 0;
I suggest to make patch small, esp. if you ask for backport to v2.6.23+.
Helge
vesafb_fix.smem_start = si->lfb_base; vesafb_defined.bits_per_pixel = si->lfb_depth; if (15 == vesafb_defined.bits_per_pixel) diff --git a/include/linux/screen_info.h b/include/linux/screen_info.h index 75303c126285a..95f2a339de329 100644 --- a/include/linux/screen_info.h +++ b/include/linux/screen_info.h @@ -49,6 +49,11 @@ static inline u64 __screen_info_lfb_size(const struct screen_info *si, unsigned return lfb_size; }
+static inline bool __screen_info_vbe_mode_nonvga(const struct screen_info *si) +{
- return si->vesa_attributes & BIT(5); // VGA if _not_ set
+}
- static inline unsigned int __screen_info_video_type(unsigned int type) { switch (type) {
Helge Deller deller@gmx.de writes:
On 6/13/24 11:02, Thomas Zimmermann wrote:
Test the vesa_attributes field in struct screen_info for compatibility with VGA hardware. Vesafb currently tests bit 1 in screen_info's capabilities field, It sets the framebuffer address size and is unrelated to VGA.
Section 4.4 of the Vesa VBE 2.0 specifications defines that bit 5 in the mode's attributes field signals VGA compatibility. The mode is compatible with VGA hardware if the bit is clear. In that case, the driver can access VGA state of the VBE's underlying hardware. The vesafb driver uses this feature to program the color LUT in palette modes. Without, colors might be incorrect.
The problem got introduced in commit 89ec4c238e7a ("[PATCH] vesafb: Fix incorrect logo colors in x86_64"). It incorrectly stores the mode attributes in the screen_info's capabilities field and updates vesafb accordingly. Later, commit 5e8ddcbe8692 ("Video mode probing support for the new x86 setup code") fixed the screen_info, but did not update vesafb. Color output still tends to work, because bit 1 in capabilities is usually 0.
Besides fixing the bug in vesafb, this commit introduces a helper that reads the correct bit from screen_info.
Nice catch, Thomas!
But do we really need this additional helper?
Signed-off-by: Thomas Zimmermann tzimmermann@suse.de Fixes: 5e8ddcbe8692 ("Video mode probing support for the new x86 setup code") Cc: stable@vger.kernel.org # v2.6.23+
drivers/video/fbdev/vesafb.c | 2 +- include/linux/screen_info.h | 5 +++++ 2 files changed, 6 insertions(+), 1 deletion(-)
diff --git a/drivers/video/fbdev/vesafb.c b/drivers/video/fbdev/vesafb.c index 8ab64ae4cad3e..5a161750a3aee 100644 --- a/drivers/video/fbdev/vesafb.c +++ b/drivers/video/fbdev/vesafb.c @@ -271,7 +271,7 @@ static int vesafb_probe(struct platform_device *dev) if (si->orig_video_isVGA != VIDEO_TYPE_VLFB) return -ENODEV;
- vga_compat = (si->capabilities & 2) ? 0 : 1;
- vga_compat = !__screen_info_vbe_mode_nonvga(si);
Instead maybe just this: ?
- /* mode is VGA-compatible if BIT 5 is _NOT_ set */
- vga_compat = (si->vesa_attributes & BIT(5)) == 0;
I suggest to make patch small, esp. if you ask for backport to v2.6.23+.
I prefer the helper. It's a static inline anyways and having it as a function makes it much easier to read / understand.
On 6/13/24 23:50, Javier Martinez Canillas wrote:
Helge Deller deller@gmx.de writes:
On 6/13/24 11:02, Thomas Zimmermann wrote:
Test the vesa_attributes field in struct screen_info for compatibility with VGA hardware. Vesafb currently tests bit 1 in screen_info's capabilities field, It sets the framebuffer address size and is unrelated to VGA.
Section 4.4 of the Vesa VBE 2.0 specifications defines that bit 5 in the mode's attributes field signals VGA compatibility. The mode is compatible with VGA hardware if the bit is clear. In that case, the driver can access VGA state of the VBE's underlying hardware. The vesafb driver uses this feature to program the color LUT in palette modes. Without, colors might be incorrect.
The problem got introduced in commit 89ec4c238e7a ("[PATCH] vesafb: Fix incorrect logo colors in x86_64"). It incorrectly stores the mode attributes in the screen_info's capabilities field and updates vesafb accordingly. Later, commit 5e8ddcbe8692 ("Video mode probing support for the new x86 setup code") fixed the screen_info, but did not update vesafb. Color output still tends to work, because bit 1 in capabilities is usually 0.
Besides fixing the bug in vesafb, this commit introduces a helper that reads the correct bit from screen_info.
Nice catch, Thomas!
But do we really need this additional helper?
Signed-off-by: Thomas Zimmermann tzimmermann@suse.de Fixes: 5e8ddcbe8692 ("Video mode probing support for the new x86 setup code") Cc: stable@vger.kernel.org # v2.6.23+
drivers/video/fbdev/vesafb.c | 2 +- include/linux/screen_info.h | 5 +++++ 2 files changed, 6 insertions(+), 1 deletion(-)
diff --git a/drivers/video/fbdev/vesafb.c b/drivers/video/fbdev/vesafb.c index 8ab64ae4cad3e..5a161750a3aee 100644 --- a/drivers/video/fbdev/vesafb.c +++ b/drivers/video/fbdev/vesafb.c @@ -271,7 +271,7 @@ static int vesafb_probe(struct platform_device *dev) if (si->orig_video_isVGA != VIDEO_TYPE_VLFB) return -ENODEV;
- vga_compat = (si->capabilities & 2) ? 0 : 1;
- vga_compat = !__screen_info_vbe_mode_nonvga(si);
Instead maybe just this: ?
- /* mode is VGA-compatible if BIT 5 is _NOT_ set */
- vga_compat = (si->vesa_attributes & BIT(5)) == 0;
I suggest to make patch small, esp. if you ask for backport to v2.6.23+.
I prefer the helper. It's a static inline anyways and having it as a function makes it much easier to read / understand.
Really?
+static inline bool __screen_info_vbe_mode_nonvga(const struct screen_info *si) +{ + return si->vesa_attributes & BIT(5); // VGA if _not_ set +}
At least the double negation "!nonvga()" breaks my head and the "//" comment should be converted to /*..*/ IMHO.
Helge
Hi
Am 14.06.24 um 00:24 schrieb Helge Deller:
On 6/13/24 23:50, Javier Martinez Canillas wrote:
Helge Deller deller@gmx.de writes:
On 6/13/24 11:02, Thomas Zimmermann wrote:
Test the vesa_attributes field in struct screen_info for compatibility with VGA hardware. Vesafb currently tests bit 1 in screen_info's capabilities field, It sets the framebuffer address size and is unrelated to VGA.
Section 4.4 of the Vesa VBE 2.0 specifications defines that bit 5 in the mode's attributes field signals VGA compatibility. The mode is compatible with VGA hardware if the bit is clear. In that case, the driver can access VGA state of the VBE's underlying hardware. The vesafb driver uses this feature to program the color LUT in palette modes. Without, colors might be incorrect.
The problem got introduced in commit 89ec4c238e7a ("[PATCH] vesafb: Fix incorrect logo colors in x86_64"). It incorrectly stores the mode attributes in the screen_info's capabilities field and updates vesafb accordingly. Later, commit 5e8ddcbe8692 ("Video mode probing support for the new x86 setup code") fixed the screen_info, but did not update vesafb. Color output still tends to work, because bit 1 in capabilities is usually 0.
Besides fixing the bug in vesafb, this commit introduces a helper that reads the correct bit from screen_info.
Nice catch, Thomas!
But do we really need this additional helper?
Yes, please. Decoding screen_info is a science on it's own. I've added several of these helpers to access because such code was open-coded and duplicated all over the graphics code. And several places got something wrong. The patch here is just one of many such cases.
Signed-off-by: Thomas Zimmermann tzimmermann@suse.de Fixes: 5e8ddcbe8692 ("Video mode probing support for the new x86 setup code") Cc: stable@vger.kernel.org # v2.6.23+
drivers/video/fbdev/vesafb.c | 2 +- include/linux/screen_info.h | 5 +++++ 2 files changed, 6 insertions(+), 1 deletion(-)
diff --git a/drivers/video/fbdev/vesafb.c b/drivers/video/fbdev/vesafb.c index 8ab64ae4cad3e..5a161750a3aee 100644 --- a/drivers/video/fbdev/vesafb.c +++ b/drivers/video/fbdev/vesafb.c @@ -271,7 +271,7 @@ static int vesafb_probe(struct platform_device *dev) if (si->orig_video_isVGA != VIDEO_TYPE_VLFB) return -ENODEV;
- vga_compat = (si->capabilities & 2) ? 0 : 1; + vga_compat = !__screen_info_vbe_mode_nonvga(si);
Instead maybe just this: ? + /* mode is VGA-compatible if BIT 5 is _NOT_ set */ + vga_compat = (si->vesa_attributes & BIT(5)) == 0;
I suggest to make patch small, esp. if you ask for backport to v2.6.23+.
I prefer the helper. It's a static inline anyways and having it as a function makes it much easier to read / understand.
Really?
Yep.
+static inline bool __screen_info_vbe_mode_nonvga(const struct screen_info *si) +{ + return si->vesa_attributes & BIT(5); // VGA if _not_ set +}
At least the double negation "!nonvga()" breaks my head and the "//" comment should be converted to /*..*/ IMHO.
The non-VGA bit is specified by VESA. So the helper does the correct thing. We can make a better comment though.
If we want to simplify usage of this helper, I'd say we should kick vga_compat from vesafb and rework that code.
Best regards Thomas
Helge
On 6/14/24 09:23, Thomas Zimmermann wrote:
Hi
Am 14.06.24 um 00:24 schrieb Helge Deller:
On 6/13/24 23:50, Javier Martinez Canillas wrote:
Helge Deller deller@gmx.de writes:
On 6/13/24 11:02, Thomas Zimmermann wrote:
Test the vesa_attributes field in struct screen_info for compatibility with VGA hardware. Vesafb currently tests bit 1 in screen_info's capabilities field, It sets the framebuffer address size and is unrelated to VGA.
Section 4.4 of the Vesa VBE 2.0 specifications defines that bit 5 in the mode's attributes field signals VGA compatibility. The mode is compatible with VGA hardware if the bit is clear. In that case, the driver can access VGA state of the VBE's underlying hardware. The vesafb driver uses this feature to program the color LUT in palette modes. Without, colors might be incorrect.
The problem got introduced in commit 89ec4c238e7a ("[PATCH] vesafb: Fix incorrect logo colors in x86_64"). It incorrectly stores the mode attributes in the screen_info's capabilities field and updates vesafb accordingly. Later, commit 5e8ddcbe8692 ("Video mode probing support for the new x86 setup code") fixed the screen_info, but did not update vesafb. Color output still tends to work, because bit 1 in capabilities is usually 0.
Besides fixing the bug in vesafb, this commit introduces a helper that reads the correct bit from screen_info.
Nice catch, Thomas!
But do we really need this additional helper?
Yes, please. Decoding screen_info is a science on it's own. I've added several of these helpers to access because such code was open-coded and duplicated all over the graphics code. And several places got something wrong. The patch here is just one of many such cases.
Signed-off-by: Thomas Zimmermann tzimmermann@suse.de Fixes: 5e8ddcbe8692 ("Video mode probing support for the new x86 setup code") Cc: stable@vger.kernel.org # v2.6.23+
drivers/video/fbdev/vesafb.c | 2 +- include/linux/screen_info.h | 5 +++++ 2 files changed, 6 insertions(+), 1 deletion(-)
diff --git a/drivers/video/fbdev/vesafb.c b/drivers/video/fbdev/vesafb.c index 8ab64ae4cad3e..5a161750a3aee 100644 --- a/drivers/video/fbdev/vesafb.c +++ b/drivers/video/fbdev/vesafb.c @@ -271,7 +271,7 @@ static int vesafb_probe(struct platform_device *dev) if (si->orig_video_isVGA != VIDEO_TYPE_VLFB) return -ENODEV;
- vga_compat = (si->capabilities & 2) ? 0 : 1; + vga_compat = !__screen_info_vbe_mode_nonvga(si);
Instead maybe just this: ? + /* mode is VGA-compatible if BIT 5 is _NOT_ set */ + vga_compat = (si->vesa_attributes & BIT(5)) == 0;
I suggest to make patch small, esp. if you ask for backport to v2.6.23+.
I prefer the helper. It's a static inline anyways and having it as a function makes it much easier to read / understand.
Really?
Yep.
+static inline bool __screen_info_vbe_mode_nonvga(const struct screen_info *si) +{ + return si->vesa_attributes & BIT(5); // VGA if _not_ set +}
At least the double negation "!nonvga()" breaks my head and the "//" comment should be converted to /*..*/ IMHO.
The non-VGA bit is specified by VESA. So the helper does the correct thing. We can make a better comment though.
If we want to simplify usage of this helper, I'd say we should kick vga_compat from vesafb and rework that code.
Ok, then I suggest to keep your patch as-is, with just the "//" comment replaced by a /**/ comment.
Helge
linux-stable-mirror@lists.linaro.org
-
Helge Deller -
Javier Martinez Canillas -
Thomas Zimmermann