linux-kernel - Re: [PATCH v3 1/4] drm/dp: Add wait_hpd_asserted() callback to struct drm_dp

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Date:   Thu, 2 Jun 2022 13:22:35 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Douglas Anderson <dianders@...omium.org>,
        dri-devel@...ts.freedesktop.org
Cc:     Hsin-Yi Wang <hsinyi@...omium.org>,
        Sankeerth Billakanti <quic_sbillaka@...cinc.com>,
        Philip Chen <philipchen@...omium.org>,
        Robert Foss <robert.foss@...aro.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Jani Nikula <jani.nikula@...el.com>,
        Kees Cook <keescook@...omium.org>,
        Lyude Paul <lyude@...hat.com>,
        Maxime Ripard <maxime@...no.tech>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/4] drm/dp: Add wait_hpd_asserted() callback to struct
 drm_dp_aux

On 18/04/2022 20:17, Douglas Anderson wrote:
> Sometimes it's useful for users of the DP AUX bus (like panels) to be
> able to poll HPD. Let's add a callback that allows DP AUX busses
> drivers to provide this.
> 
> Suggested-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> Signed-off-by: Douglas Anderson <dianders@...omium.org>

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>


> ---
> Left Dmitry's Reviewed-by tag off since patch changed enough.
> 
> (no changes since v2)
> 
> Changes in v2:
> - Change is_hpd_asserted() to wait_hpd_asserted()
> 
>   include/drm/dp/drm_dp_helper.h | 26 ++++++++++++++++++++++++++
>   1 file changed, 26 insertions(+)
> 
> diff --git a/include/drm/dp/drm_dp_helper.h b/include/drm/dp/drm_dp_helper.h
> index 53d1e722f4de..0940c415db8c 100644
> --- a/include/drm/dp/drm_dp_helper.h
> +++ b/include/drm/dp/drm_dp_helper.h
> @@ -2035,6 +2035,32 @@ struct drm_dp_aux {
>   	ssize_t (*transfer)(struct drm_dp_aux *aux,
>   			    struct drm_dp_aux_msg *msg);
>   
> +	/**
> +	 * @wait_hpd_asserted: wait for HPD to be asserted
> +	 *
> +	 * This is mainly useful for eDP panels drivers to wait for an eDP
> +	 * panel to finish powering on. This is an optional function.
> +	 *
> +	 * This function will efficiently wait for up to `wait_us` microseconds
> +	 * for HPD to be asserted and might sleep.
> +	 *
> +	 * This function returns 0 if HPD was asserted or -ETIMEDOUT if time
> +	 * expired and HPD wasn't asserted. This function should not print
> +	 * timeout errors to the log.
> +	 *
> +	 * The semantics of this function are designed to match the
> +	 * readx_poll_timeout() function. That means a `wait_us` of 0 means
> +	 * to wait forever. If you want to do a quick poll you could pass 1
> +	 * for `wait_us`.
> +	 *
> +	 * NOTE: this function specifically reports the state of the HPD pin
> +	 * that's associated with the DP AUX channel. This is different from
> +	 * the HPD concept in much of the rest of DRM which is more about
> +	 * physical presence of a display. For eDP, for instance, a display is
> +	 * assumed always present even if the HPD pin is deasserted.
> +	 */
> +	int (*wait_hpd_asserted)(struct drm_dp_aux *aux, unsigned long wait_us);
> +
>   	/**
>   	 * @i2c_nack_count: Counts I2C NACKs, used for DP validation.
>   	 */


-- 
With best wishes
Dmitry