linux-kernel - Re: [PATCH v5 17/24] drm/msm/dsi/phy: Fix missing initial VCO rate

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Message-ID: <sz4kbwy5nwsebgf64ia7uq4ee7wbsa5uy3xmlqwcstsbntzcov@ew3dcyjdzmi2>
Date: Sat, 3 May 2025 01:48:14 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc: 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>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Krishna Manikandan <quic_mkrishn@...cinc.com>,
        Jonathan Marek <jonathan@...ek.ca>,
        Kuogee Hsieh <quic_khsieh@...cinc.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Dmitry Baryshkov <lumag@...nel.org>, Rob Clark <robdclark@...il.com>,
        Bjorn Andersson <andersson@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>, linux-arm-msm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Rob Clark <robdclark@...omium.org>, linux-clk@...r.kernel.org,
        Srinivas Kandagatla <srini@...nel.org>
Subject: Re: [PATCH v5 17/24] drm/msm/dsi/phy: Fix missing initial VCO rate

On Wed, Apr 30, 2025 at 03:00:47PM +0200, Krzysztof Kozlowski wrote:
> Driver unconditionally saves current state on first init in
> dsi_pll_7nm_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_7nm_pll_restore_state().
> 
> Restoring calls dsi_pll_7nm_vco_set_rate() with
> pll_7nm->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.
> 
> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
> 
> ---
> 
> Changes in v5:
> 1. New patch
> ---
>  drivers/gpu/drm/msm/dsi/phy/dsi_phy_7nm.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>

Please implement similar change into the 10nm driver.

An alternative approach might be to do something like (14nm):

        cached_state->vco_rate = clk_hw_get_rate(phy->vco_hw);


-- 
With best wishes
Dmitry