[Freedreno] db820: smmu clocks issue in kernel

[Pradeep Reddy]

On Tue, Aug 14, 2018 at 8:07 PM, Rob Clark <robdclark at gmail.com> wrote:

> On Tue, Aug 14, 2018 at 9:00 AM Pradeep Reddy
> <pradeep.mundlapudi5 at gmail.com> wrote:
> >
> > Hi Archit,
> >
> > I have enabled splash screen (penguin) in bootloader with fastboot oem
> select-display-panel hdmi. Kernel crashes during boot. I identified that
> there is issue with below two smmu clocks.
> > static struct clk_branch smmu_mdp_ahb_clk = {
> >         .halt_reg = 0x2454,
> >         .clkr = {
> >                 .enable_reg = 0x2454,
> >                 .enable_mask = BIT(0),
> >
> > static struct clk_branch smmu_mdp_axi_clk = {
> >         .halt_reg = 0x2458,
> >         .clkr = {
> >                 .enable_reg = 0x2458,
> >                 .enable_mask = BIT(0),
> >
> > I tried to reset the clocks in mmcc_msm8996_probe, with the below
> changes.
> >        regmap_update_bits(regmap, 0x2454, BIT(0), 0);
> >         regmap_update_bits(regmap, 0x2458, BIT(0), 0);
> >
> > Then i don't see a kernel crash but blue screen appears after penguin
> for some time. Then HDMI display comes up.
> >
> > Can you please let me know better way to reset smmu clocks?
> >
>
> tbh, this is probably the tip of the iceberg.. It is going to take a
> fair bit of work to make this work properly, especially with something
> like hdmi were we need to readback hw state to figure out display
> timings.  I started something a year or so back on db410c, but it
> needs some clk framework changes and some gdsc changes.  I'm not sure
> anyone has had a chance to pick up this work since then.
>
> Do you *really* need to enable the display from the bootloader.  By
> *far* the easiest solution is to not do that.
>
> Thanks Rob, for detailed  explanation.
Some of Android users use hdmi as primary display. when they switch to
linux, they face kernel crash.
we suggest them to run the command 'fastboot oem select-display-panel'
(blank string).
so, thought to come up with better solution.

Thanks,
Pradeep

BR,
> -R
>
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