Re: [PATCH] drm/bridge/synopsys: dsi: use adjusted_mode in mode_set

[Philippe CORNU]

Hi Brian,
And a big thanks for your Tested-by

On 01/25/2018 11:47 PM, Brian Norris wrote:
> On Thu, Jan 25, 2018 at 7:55 AM, Philippe Cornu <philippe.cornu@xxxxxx> wrote:
>> The "adjusted_mode" clock value (ie the real pixel clock) is more
>> accurate than "mode" clock value (ie the panel/bridge requested
>> clock value). It offers a better preciseness for timing
>> computations and allows to reduce the extra dsi bandwidth in
>> burst mode (from ~20% to ~10-12%, hw platform dependant).
>>
>> Signed-off-by: Philippe Cornu <philippe.cornu@xxxxxx>
>> ---
>> Note: This patch replaces "drm/bridge/synopsys: dsi: add optional pixel clock"
> 
> These two appear to be the same for my cases, but at least nothing breaks:
> 

In drivers/gpu/drm/rockchip/rockchip_drm_vop.c function 
vop_crtc_mode_fixup(), the adjusted_mode->clock (ie. vop px clk output = 
dw dsi px clk input) is updated according to rockchip hw pll/dividers...

So you "may" have a different value in adjusted_mode->clock compare to 
mode->clock. Maybe there is no difference for the panel you are using 
because its px clock matches perfectly with rockchip hw pll/dividers... 
or has been set to match with ;-)

I did a similar patch (see [1]) and it works "fine" on stm, the only 
difference with the rockchip vop is that clk_round_rate() returns odd 
values on stm so I used set/get_rate instead.

So now, both rockchip & stm crtc have an "adjusted_mode->clock" so it 
makes sense to use it in dw dsi :)

Philippe :-)

[1] https://patchwork.freedesktop.org/patch/200720/
"[PATCH] drm/stm: ltdc: use crtc_mode_fixup to update adjusted_mode clock"


> Tested-by: Brian Norris <briannorris@xxxxxxxxxxxx>
>