linux-kernel - Re: [PATCH v2 08/10] drm/bridge: anx7625: enable HPD interrupts

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Message-ID: <lkeezxmjs6qn36qzhmvmtngvrxuwng53rgcb75centx6ds5h4d@dx2iz4aqrcho>
Date: Fri, 21 Mar 2025 19:37:31 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Ayushi Makhija <quic_amakhija@...cinc.com>
Cc: Dmitry Baryshkov <lumag@...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,
        robdclark@...il.com, dmitry.baryshkov@...aro.org, sean@...rly.run,
        marijn.suijten@...ainline.org, andersson@...nel.org, robh@...nel.org,
        robh+dt@...nel.org, krzk+dt@...nel.org, konradybcio@...nel.org,
        conor+dt@...nel.org, andrzej.hajda@...el.com,
        neil.armstrong@...aro.org, rfoss@...nel.org,
        Laurent.pinchart@...asonboard.com, jonas@...boo.se,
        jernej.skrabec@...il.com, quic_abhinavk@...cinc.com,
        quic_rajeevny@...cinc.com, quic_vproddut@...cinc.com,
        quic_jesszhan@...cinc.com
Subject: Re: [PATCH v2 08/10] drm/bridge: anx7625: enable HPD interrupts

On Fri, Mar 21, 2025 at 02:36:21AM +0530, Ayushi Makhija wrote:
> On 3/11/2025 9:09 PM, Dmitry Baryshkov wrote:
> > On Tue, Mar 11, 2025 at 05:54:43PM +0530, Ayushi Makhija wrote:
> >> When device enters the suspend state, it prevents
> >> HPD interrupts from occurring. To address this,
> >> add an additional PM runtime vote in hpd_enable().
> >> This vote is removed in hpd_disable().
> > 
> > Is it really enough to toggle the HPD interrupts? Is there any kind of
> > programming that should be moved to .hpd_enable() too (so that by
> > default the bridge doesn't generate HPD interrupts)?
> > 
> 
> Hi Dmirty,
> 
> I couldn't find the ANX7625 bridge driver datasheet, where all the registers information are present.
> 
> As per my understanding, we have anx7625_hpd_timer_config(), where debounce timer registers are getting set, which help to manage the detection and stability of the HPD signal.
> 
> anx7625_hpd_timer_config() is getting called from anx7625_runtime_pm_resume().
> 
> anx7625_runtime_pm_resume
>    anx7625_power_on_init
>        anx7625_ocm_loading_check
>            anx7625_disable_pd_protocol
>               anx7625_hpd_timer_config
> 
> So, I think HPD programming is already taken care in anx7625_hpd_timer_config(). anx7625_runtime_pm_resume() is getting called for both eDP and DP configuration. 
> 
> If you suggest then, I can move the anx7625_hpd_timer_config() from anx7625_disable_pd_protocol() to anx7625_bridge_hpd_enable().

This might result in HPD signal being generated after invalid or
improper timings. If we can't get a feedback from Analogix on how to
control HPD generation, then it's better to leave it as is.

-- 
With best wishes
Dmitry