Re: [PATCH V2 5/6] drm: bridge: samsung-dsim: Support non-burst mode

[Marek Szyprowski]

On 24.04.2023 12:00, Adam Ford wrote:
> On Mon, Apr 24, 2023 at 3:25 AM Marek Szyprowski
> <m.szyprowski@xxxxxxxxxxx> wrote:
>> On 23.04.2023 14:12, Adam Ford wrote:
>>> The high-speed clock is hard-coded to the burst-clock
>>> frequency specified in the device tree.  However, when
>>> using devices like certain bridge chips without burst mode
>>> and varying resolutions and refresh rates, it may be
>>> necessary to set the high-speed clock dynamically based
>>> on the desired pixel clock for the connected device.
>>>
>>> This also removes the need to set a clock speed from
>>> the device tree for non-burst mode operation, since the
>>> pixel clock rate is the rate requested from the attached
>>> device like an HDMI bridge chip.  This should have no
>>> impact for people using burst-mode and setting the burst
>>> clock rate is still required for those users.
>>>
>>> Signed-off-by: Adam Ford <aford173@xxxxxxxxx>
>> This one breaks Exynos-5433 based TM2e board with a DSI panel.
> Marek S,
>
> Thank you for testing!  I knoiw there are several of us who appreciate
> your testing this since it's hard to know if something broke without
> hardware.  Is there any way you can tell me if the flag is set to
> enable MIPI_DSI_MODE_VIDEO_BURST?

TM2e board uses the DSI panel operated in command mode and handled by 
panel-samsung-s6e3ha2.c driver. The MIPI_DSI_MODE_VIDEO_BURST flag is 
not set by the driver. However, the MIPI_DSI_CLOCK_NON_CONTINUOUS flags 
is set there. I really have no idea if setting VIDEO_BURST would make 
sense together with CLOCK_NON_CONTINUOUS or not. Maybe the driver lacks 
setting it?


> I was trying to be diligent about not breaking your boards, but
> without your boards, it's difficult.  The theory was that if
> MIPI_DSI_MODE_VIDEO_BURST is set and there is a burst clock set in the
> device tree, it would use the burst clock.
>
> As a fall-back I could just simply check for the presence of the
> burst_clock_rate instead of both MIPI_DSI_MODE_VIDEO_BURST and
> burst_clock_rate.

Maybe you should extend your check also for the 
MIPI_DSI_CLOCK_NON_CONTINUOUS flag? Does it make sense?

 > ...

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland