linux-kernel - Re: [PATCH v7 09/15] drm/bridge: analogix_dp: Add support to get panel from the DP AUX bus

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Message-ID: <CAD=FV=WoigDDTG6wTK0smsxASVfK5BzzW6KNpKWq97v4GAgvmw@mail.gmail.com>
Date: Mon, 24 Feb 2025 17:41:17 -0800
From: Doug Anderson <dianders@...omium.org>
To: Damon Ding <damon.ding@...k-chips.com>
Cc: heiko@...ech.de, andy.yan@...k-chips.com, hjc@...k-chips.com, 
	robh@...nel.org, krzk+dt@...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, 
	dmitry.baryshkov@...aro.org, sebastian.reichel@...labora.com, 
	cristian.ciocaltea@...labora.com, boris.brezillon@...labora.com, 
	l.stach@...gutronix.de, dri-devel@...ts.freedesktop.org, 
	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 09/15] drm/bridge: analogix_dp: Add support to get
 panel from the DP AUX bus

Hi,

On Mon, Feb 24, 2025 at 12:14 AM Damon Ding <damon.ding@...k-chips.com> wrote:
>
> The main modification is moving the DP AUX initialization from function
> analogix_dp_bind() to analogix_dp_probe(). In order to get the EDID of
> eDP panel during probing, it is also needed to advance PM operations to
> ensure that eDP controller and phy are prepared for AUX transmission.
>
> Additionally, add support for &drm_dp_aux.wait_hpd_asserted() to help
> confirm the HPD state before doing AUX transfers.

Maybe move the addition of the analogix_dpaux_wait_hpd_asserted() to a
separate patch?


> Signed-off-by: Damon Ding <damon.ding@...k-chips.com>
>
> ---
>
> Changes in v4:
> - Use done_probing() to call drm_of_find_panel_or_bridge() and
>   component_add() when getting panel from the DP AUX bus
>
> Changes in v5:
> - Advance PM operations to make eDP AUX work well
>
> Changes in v6:
> - Use devm_pm_runtime_enable() instead of devm_add_action_or_reset()
> - Add a new function analogix_dp_remove() to ensure symmetry for PM
>   operations
>
> Changes in v7:
> - Fix the misspelling of word 'operations' in commit message
> - Remove the check related to CONFIG_PM
> - Remove the unnecessary call to pm_runtime_dont_use_autosuspend() if
>   devm_pm_runtime_enable() fails
> - Remove unnecessary function analogix_dp_remove()
> - Add new function analogix_dpaux_wait_hpd_asserted()
> ---
>  .../drm/bridge/analogix/analogix_dp_core.c    | 37 ++++++++++++++-----
>  1 file changed, 28 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
> index a57e06d303a1..ff81c37dbe1d 100644
> --- a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
> +++ b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
> @@ -1548,6 +1548,22 @@ static ssize_t analogix_dpaux_transfer(struct drm_dp_aux *aux,
>         return ret;
>  }
>
> +static int analogix_dpaux_wait_hpd_asserted(struct drm_dp_aux *aux, unsigned long wait_us)
> +{
> +       struct analogix_dp_device *dp = to_dp(aux);
> +       int val;
> +       int ret;
> +
> +       pm_runtime_get_sync(dp->dev);
> +
> +       ret = readx_poll_timeout(analogix_dp_detect_hpd, dp, val, !val, wait_us / 100, wait_us);

More than happy if someone else wants to overrule me, but it seems
weird that you're looping over a function that already has a loop.
Shouldn't you be calling analogix_dp_get_plug_in_status() directly?
...and if "dp->force_hpd" you probably shouldn't be polling at all. If
HPD is not hooked up I think we decided in sn65dsi86 that we should
just sleep for the maximum time (choosing a conservative value if told
to wait forever).


Aside from that and the idea of moving
analogix_dpaux_wait_hpd_asserted() to a separate patch this looks good
to me.


-Doug