From: maxime@cerno.tech maxime@cerno.tech
[ Upstream commit 3bc6a37f59f21a8bfaf74d0975b2eb0b2d52a065 ]
Commit ae71ab585c81 ("drm/vc4: hdmi: Enforce the minimum rate at runtime_resume") reintroduced the call to clk_set_min_rate in an attempt to fix the boot without a monitor connected on the RaspberryPi3.
However, that introduced a regression breaking the display output entirely (black screen but no vblank timeout) on the Pi4.
This is due to the fact that we now have in a typical modeset at boot, in vc4_hdmi_encoder_pre_crtc_configure(), we have a first call to clk_set_min_rate() asking for the minimum rate of the HSM clock for our given resolution, and then a call to pm_runtime_resume_and_get(). We will thus execute vc4_hdmi_runtime_resume() which, since the commit mentioned above, will call clk_set_min_rate() a second time with the absolute minimum rate we want to enforce on the HSM clock.
We're thus effectively erasing the minimum mandated by the mode we're trying to set. The fact that only the Pi4 is affected is due to the fact that it uses a different clock driver that tries to minimize the HSM clock at all time. It will thus lower the HSM clock rate to 120MHz on the second clk_set_min_rate() call.
The Pi3 doesn't use the same driver and will not change the frequency on the second clk_set_min_rate() call since it's still within the new boundaries and it doesn't have the code to minimize the clock rate as needed. So even though the boundaries are still off, the clock rate is still the right one for our given mode, so everything works.
There is a lot of moving parts, so I couldn't find any obvious solution:
- Reverting the original is not an option, as that would break the Pi3 again.
- We can't move the clk_set_min_rate() call in _pre_crtc_configure() since because, on the Pi3, the HSM clock has the CLK_SET_RATE_GATE flag which prevents the clock rate from being changed after it's been enabled. Our calls to clk_set_min_rate() can change it, so they need to be done before clk_prepare_enable().
- We can't remove the call to clk_prepare_enable() from the runtime_resume hook to put it into _pre_crtc_configure() either, since we need that clock to be enabled to access the registers, and we can't count on the fact that the display will be active in all situations (doing any CEC operation, or listing the modes while inactive are valid for example()).
- We can't drop the call to clk_set_min_rate() in _pre_crtc_configure() since we would need to still enforce the minimum rate for a given resolution, and runtime_resume doesn't have access to the current mode, if there's any.
- We can't copy the TMDS character rate into vc4_hdmi and reuse it since, because it's part of the KMS atomic state, it needs to be protected by a mutex. Unfortunately, some functions (CEC operations, mostly) can be reentrant (through the CEC framework) and still need a pm_runtime_get.
However, we can work around this issue by leveraging the fact that the clk_set_min_rate() calls set boundaries for its given struct clk, and that each different clk_get() call will return a different instance of struct clk. The clock framework will then aggregate the boundaries for each struct clk instances linked to a given clock, plus its hardware boundaries, and will use that.
We can thus get an extra HSM clock user for runtime_pm use only, and use our different clock instances depending on the context: runtime_pm will use its own to set the absolute minimum clock setup so that we never lock the CPU waiting for a register access, and the modeset part will set its requirement for the current resolution. And we let the CCF do the coordination.
It's not an ideal solution, but it's fairly unintrusive and doesn't really change any part of the logic so it looks like a rather safe fix.
Link: https://bugzilla.redhat.com/show_bug.cgi?id=2136234 Fixes: ae71ab585c81 ("drm/vc4: hdmi: Enforce the minimum rate at runtime_resume") Reported-by: Peter Robinson pbrobinson@gmail.com Reviewed-by: Javier Martinez Canillas javierm@redhat.com Tested-by: Peter Robinson pbrobinson@gmail.com Link: https://lore.kernel.org/r/20221021131339.2203291-1-maxime@cerno.tech Signed-off-by: Maxime Ripard maxime@cerno.tech Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/gpu/drm/vc4/vc4_hdmi.c | 21 +++++++++++++++++---- drivers/gpu/drm/vc4/vc4_hdmi.h | 1 + 2 files changed, 18 insertions(+), 4 deletions(-)
diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c index 874c6bd787c5..4e5bba0822a5 100644 --- a/drivers/gpu/drm/vc4/vc4_hdmi.c +++ b/drivers/gpu/drm/vc4/vc4_hdmi.c @@ -2712,9 +2712,16 @@ static int vc4_hdmi_init_resources(struct vc4_hdmi *vc4_hdmi) DRM_ERROR("Failed to get HDMI state machine clock\n"); return PTR_ERR(vc4_hdmi->hsm_clock); } + vc4_hdmi->audio_clock = vc4_hdmi->hsm_clock; vc4_hdmi->cec_clock = vc4_hdmi->hsm_clock;
+ vc4_hdmi->hsm_rpm_clock = devm_clk_get(dev, "hdmi"); + if (IS_ERR(vc4_hdmi->hsm_rpm_clock)) { + DRM_ERROR("Failed to get HDMI state machine clock\n"); + return PTR_ERR(vc4_hdmi->hsm_rpm_clock); + } + return 0; }
@@ -2796,6 +2803,12 @@ static int vc5_hdmi_init_resources(struct vc4_hdmi *vc4_hdmi) return PTR_ERR(vc4_hdmi->hsm_clock); }
+ vc4_hdmi->hsm_rpm_clock = devm_clk_get(dev, "hdmi"); + if (IS_ERR(vc4_hdmi->hsm_rpm_clock)) { + DRM_ERROR("Failed to get HDMI state machine clock\n"); + return PTR_ERR(vc4_hdmi->hsm_rpm_clock); + } + vc4_hdmi->pixel_bvb_clock = devm_clk_get(dev, "bvb"); if (IS_ERR(vc4_hdmi->pixel_bvb_clock)) { DRM_ERROR("Failed to get pixel bvb clock\n"); @@ -2859,7 +2872,7 @@ static int vc4_hdmi_runtime_suspend(struct device *dev) { struct vc4_hdmi *vc4_hdmi = dev_get_drvdata(dev);
- clk_disable_unprepare(vc4_hdmi->hsm_clock); + clk_disable_unprepare(vc4_hdmi->hsm_rpm_clock);
return 0; } @@ -2877,11 +2890,11 @@ static int vc4_hdmi_runtime_resume(struct device *dev) * its frequency while the power domain is active so that it * keeps its rate. */ - ret = clk_set_min_rate(vc4_hdmi->hsm_clock, HSM_MIN_CLOCK_FREQ); + ret = clk_set_min_rate(vc4_hdmi->hsm_rpm_clock, HSM_MIN_CLOCK_FREQ); if (ret) return ret;
- ret = clk_prepare_enable(vc4_hdmi->hsm_clock); + ret = clk_prepare_enable(vc4_hdmi->hsm_rpm_clock); if (ret) return ret;
@@ -2894,7 +2907,7 @@ static int vc4_hdmi_runtime_resume(struct device *dev) * case, it will lead to a silent CPU stall. Let's make sure we * prevent such a case. */ - rate = clk_get_rate(vc4_hdmi->hsm_clock); + rate = clk_get_rate(vc4_hdmi->hsm_rpm_clock); if (!rate) { ret = -EINVAL; goto err_disable_clk; diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.h b/drivers/gpu/drm/vc4/vc4_hdmi.h index c3ed2b07df23..47f141ec8c40 100644 --- a/drivers/gpu/drm/vc4/vc4_hdmi.h +++ b/drivers/gpu/drm/vc4/vc4_hdmi.h @@ -171,6 +171,7 @@ struct vc4_hdmi { struct clk *cec_clock; struct clk *pixel_clock; struct clk *hsm_clock; + struct clk *hsm_rpm_clock; struct clk *audio_clock; struct clk *pixel_bvb_clock;