linux-kernel - Re: [PATCH] drm/bridge/synopsys: dsi: use adjusted_mode in mode

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Message-ID: <5f9d5de7-4597-b9e9-64fe-666230b12bce@st.com>
Date:   Fri, 26 Jan 2018 09:54:01 +0000
From:   Philippe CORNU <philippe.cornu@...com>
To:     Brian Norris <briannorris@...omium.org>
CC:     Archit Taneja <architt@...eaurora.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        David Airlie <airlied@...ux.ie>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Bhumika Goyal <bhumirks@...il.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "Linux Kernel" <linux-kernel@...r.kernel.org>,
        Sandy Huang <hjc@...k-chips.com>,
        Heiko Stubner <heiko@...ech.de>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        Yannick FERTRE <yannick.fertre@...com>,
        Vincent ABRIOU <vincent.abriou@...com>,
        Alexandre TORGUE <alexandre.torgue@...com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Ludovic BARRE <ludovic.barre@...com>,
        Mickael REULIER <mickael.reulier@...com>
Subject: Re: [PATCH] drm/bridge/synopsys: dsi: use adjusted_mode in mode_set

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@...com> 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@...com>
>> ---
>> 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@...omium.org>
>