linux-kernel - Re: [PATCH] drm/msm/dsi/dsi_phy_10nm: Fix missing initial VCO rate

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Message-ID: <87af51dd-a35c-460a-af4c-813427cdaf84@linaro.org>
Date: Wed, 21 May 2025 08:09:14 +0200
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Cc: Rob Clark <robdclark@...il.com>, Abhinav Kumar
 <quic_abhinavk@...cinc.com>, Sean Paul <sean@...rly.run>,
 Marijn Suijten <marijn.suijten@...ainline.org>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/msm/dsi/dsi_phy_10nm: Fix missing initial VCO rate

On 20/05/2025 22:06, Dmitry Baryshkov wrote:
> On Tue, May 20, 2025 at 01:13:26PM +0200, Krzysztof Kozlowski wrote:
>> Driver unconditionally saves current state on first init in
>> dsi_pll_10nm_init(), but does not save the VCO rate, only some of the
>> divider registers.  The state is then restored during probe/enable via
>> msm_dsi_phy_enable() -> msm_dsi_phy_pll_restore_state() ->
>> dsi_10nm_pll_restore_state().
>>
>> Restoring calls dsi_pll_10nm_vco_set_rate() with
>> pll_10nm->vco_current_rate=0, which basically overwrites existing rate of
>> VCO and messes with clock hierarchy, by setting frequency to 0 to clock
>> tree.  This makes anyway little sense - VCO rate was not saved, so
>> should not be restored.
>>
>> If PLL was not configured configure it to minimum rate to avoid glitches
>> and configuring entire in clock hierarchy to 0 Hz.
>>
>> Suggested-by: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
>> Link: https://lore.kernel.org/r/sz4kbwy5nwsebgf64ia7uq4ee7wbsa5uy3xmlqwcstsbntzcov@ew3dcyjdzmi2/
>> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
> 
> Fixes?

Probably:
Fixes: a4ccc37693a2 ("drm/msm/dsi_pll_10nm: restore VCO rate during
restore_state")

But CC stable would not be appropriate, since this was never reproduced
on this PHY/hardware and we only guess a visible issue being fixed here.


Best regards,
Krzysztof