On Wed, Oct 2, 2019 at 7:25 AM Tomi Valkeinen tomi.valkeinen@ti.com wrote:

The OMAP36xx and AM/DM37x TRMs say that the maximum divider for DSS fclk (in CM_CLKSEL_DSS) is 32. Experimentation shows that this is not correct, and using divider of 32 breaks DSS with a flood or underflows and sync losts. Dividers up to 31 seem to work fine.

There is another patch to the DT files to limit the divider correctly, but as the DSS driver also needs to know the maximum divider to be able to iteratively find good rates, we also need to do the fix in the DSS driver.

When combined with the cock divider patch [1], this fixes a hanging issue on a DM3730 with a 480x272 screen where the pixel clock is set to 9MHz and the clock divider attempts to calculate a fclk and hangs. I have always had to hack the divider to prevent the hang.

If possible, it would be nice to have this applied to 5.4 branch since it will be an LTS kernel.

[1] - https://patchwork.kernel.org/cover/11170951/

Tested-by: Adam Ford aford173@gmail.com

Signed-off-by: Tomi Valkeinen tomi.valkeinen@ti.com Cc: Adam Ford aford173@gmail.com Cc: stable@vger.kernel.org

---

drivers/gpu/drm/omapdrm/dss/dss.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/omapdrm/dss/dss.c b/drivers/gpu/drm/omapdrm/dss/dss.c index e226324adb69..4bdd63b57100 100644 --- a/drivers/gpu/drm/omapdrm/dss/dss.c +++ b/drivers/gpu/drm/omapdrm/dss/dss.c @@ -1083,7 +1083,7 @@ static const struct dss_features omap34xx_dss_feats = {

static const struct dss_features omap3630_dss_feats = { .model = DSS_MODEL_OMAP3,

•   .fck_div_max            =       32,
  

•   .fck_div_max            =       31,
    .fck_freq_max           =       173000000,
    .dss_fck_multiplier     =       1,
    .parent_clk_name        =       "dpll4_ck",
  

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On Wed, Oct 2, 2019 at 7:25 AM Tomi Valkeinen tomi.valkeinen@ti.com wrote:

The OMAP36xx and AM/DM37x TRMs say that the maximum divider for DSS fclk (in CM_CLKSEL_DSS) is 32. Experimentation shows that this is not correct, and using divider of 32 breaks DSS with a flood or underflows and sync losts. Dividers up to 31 seem to work fine.

There is another patch to the DT files to limit the divider correctly, but as the DSS driver also needs to know the maximum divider to be able to iteratively find good rates, we also need to do the fix in the DSS driver.

Tomi,

Is there any way you can do a patch for the FB version for the older 4.9 and 4.14 kernels? I think they are still defaulting to the omapfb instead of DRM, so the underflow issue still appears by default and the patch only impacts the DRM version of the driver. If not, do you have any objections if I submit a patch to stable for those two LTS branches?

thanks,

adam

Signed-off-by: Tomi Valkeinen tomi.valkeinen@ti.com Cc: Adam Ford aford173@gmail.com Cc: stable@vger.kernel.org

---

drivers/gpu/drm/omapdrm/dss/dss.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/omapdrm/dss/dss.c b/drivers/gpu/drm/omapdrm/dss/dss.c index e226324adb69..4bdd63b57100 100644 --- a/drivers/gpu/drm/omapdrm/dss/dss.c +++ b/drivers/gpu/drm/omapdrm/dss/dss.c @@ -1083,7 +1083,7 @@ static const struct dss_features omap34xx_dss_feats = {

static const struct dss_features omap3630_dss_feats = { .model = DSS_MODEL_OMAP3,

•   .fck_div_max            =       32,
  

•   .fck_div_max            =       31,
    .fck_freq_max           =       173000000,
    .dss_fck_multiplier     =       1,
    .parent_clk_name        =       "dpll4_ck",
  

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