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Subject: Re: [PATCH v6 27/30] drm/rockchip: psr: Sanitize semantics of
 allow/disallow API
To:     Enric Balletbo i Serra <enric.balletbo@collabora.com>,
        architt@codeaurora.org, inki.dae@samsung.com,
        thierry.reding@gmail.com, hjc@rock-chips.com,
        seanpaul@chromium.org, airlied@linux.ie, tfiga@chromium.org,
        heiko@sntech.de
Cc:     dri-devel@lists.freedesktop.org, dianders@chromium.org,
        ykk@rock-chips.com, kernel@collabora.com, m.szyprowski@samsung.com,
        linux-samsung-soc@vger.kernel.org, jy0922.shim@samsung.com,
        rydberg@bitmath.org, krzk@kernel.org,
        linux-rockchip@lists.infradead.org, kgene@kernel.org,
        linux-input@vger.kernel.org, orjan.eide@arm.com,
        wxt@rock-chips.com, jeffy.chen@rock-chips.com,
        linux-arm-kernel@lists.infradead.org, mark.yao@rock-chips.com,
        wzz@rock-chips.com, hl@rock-chips.com, jingoohan1@gmail.com,
        sw0312.kim@samsung.com, linux-kernel@vger.kernel.org,
        kyungmin.park@samsung.com, Laurent.pinchart@ideasonboard.com,
        kuankuan.y@gmail.com, hshi@chromium.org
From:   Andrzej Hajda <a.hajda@samsung.com>
Message-ID: <fdd3e03d-a423-ea90-a13b-f124ec9afae0@samsung.com>
Date:   Mon, 16 Apr 2018 11:26:26 +0200
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On 05.04.2018 11:49, Enric Balletbo i Serra wrote:
> From: Tomasz Figa <tfiga@chromium.org>
>
> Currently both rockchip_drm_psr_activate() and _deactivate() only set the
> boolean "active" flag without actually making sure that hardware state
> complies with it.
>
> Since we are going to extend the usage of this API to properly lock PSR
> for the duration of atomic commits, we change the semantics in following
> way:
>  - a counter is used to track the number of disallow requests,
>  - PSR is actually disabled in hardware on first disallow request,
>  - PSR enable work is scheduled on last disallow request.

I guess you meant "on last allow request".
I think It would be more readable if you replace disallow with inhibit.

>
> The above allows using the API as a way to deterministically synchronize
> PSR state changes with other DRM events, i.e. atomic commits and cursor
> updates. As a nice side effect, the naming is sorted out and we have
> "inhibit" for stopping the software logic and "enable" for hardware
> state.
>
> Signed-off-by: Tomasz Figa <tfiga@chromium.org>
> Signed-off-by: Thierry Escande <thierry.escande@collabora.com>
> Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
> Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
> ---
>
>  drivers/gpu/drm/rockchip/analogix_dp-rockchip.c |  4 +-
>  drivers/gpu/drm/rockchip/rockchip_drm_psr.c     | 57 ++++++++++++++++++-------
>  drivers/gpu/drm/rockchip/rockchip_drm_psr.h     |  4 +-
>  3 files changed, 46 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/gpu/drm/rockchip/analogix_dp-rockchip.c b/drivers/gpu/drm/rockchip/analogix_dp-rockchip.c
> index 6d45d62466b3..080f05352195 100644
> --- a/drivers/gpu/drm/rockchip/analogix_dp-rockchip.c
> +++ b/drivers/gpu/drm/rockchip/analogix_dp-rockchip.c
> @@ -134,7 +134,7 @@ static int rockchip_dp_poweron_end(struct analogix_dp_plat_data *plat_data)
>  {
>  	struct rockchip_dp_device *dp = to_dp(plat_data);
>  
> -	return rockchip_drm_psr_activate(&dp->encoder);
> +	return rockchip_drm_psr_inhibit_put(&dp->encoder);
>  }
>  
>  static int rockchip_dp_powerdown(struct analogix_dp_plat_data *plat_data)
> @@ -142,7 +142,7 @@ static int rockchip_dp_powerdown(struct analogix_dp_plat_data *plat_data)
>  	struct rockchip_dp_device *dp = to_dp(plat_data);
>  	int ret;
>  
> -	ret = rockchip_drm_psr_deactivate(&dp->encoder);
> +	ret = rockchip_drm_psr_inhibit_get(&dp->encoder);
>  	if (ret != 0)
>  		return ret;
>  
> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_psr.c b/drivers/gpu/drm/rockchip/rockchip_drm_psr.c
> index 448c5fde241c..e7e16d92d5a1 100644
> --- a/drivers/gpu/drm/rockchip/rockchip_drm_psr.c
> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_psr.c
> @@ -27,7 +27,7 @@ struct psr_drv {
>  	struct drm_encoder	*encoder;
>  
>  	struct mutex		lock;
> -	bool			active;
> +	int			inhibit_count;
>  	bool			enabled;
>  
>  	struct delayed_work	flush_work;
> @@ -76,7 +76,7 @@ static int psr_set_state_locked(struct psr_drv *psr, bool enable)
>  {
>  	int ret;
>  
> -	if (!psr->active)
> +	if (psr->inhibit_count > 0)
>  		return -EINVAL;
>  
>  	if (enable == psr->enabled)
> @@ -101,13 +101,18 @@ static void psr_flush_handler(struct work_struct *work)
>  }
>  
>  /**
> - * rockchip_drm_psr_activate - activate PSR on the given pipe
> + * rockchip_drm_psr_inhibit_put - release PSR inhibit on given encoder
>   * @encoder: encoder to obtain the PSR encoder
>   *
> + * Decrements PSR inhibit count on given encoder. Should be called only
> + * for a PSR inhibit count increment done before. If PSR inhibit counter
> + * reaches zero, PSR flush work is scheduled to make the hardware enter
> + * PSR mode in PSR_FLUSH_TIMEOUT_MS.
> + *
>   * Returns:
>   * Zero on success, negative errno on failure.
>   */
> -int rockchip_drm_psr_activate(struct drm_encoder *encoder)
> +int rockchip_drm_psr_inhibit_put(struct drm_encoder *encoder)
>  {
>  	struct psr_drv *psr = find_psr_by_encoder(encoder);
>  
> @@ -115,21 +120,29 @@ int rockchip_drm_psr_activate(struct drm_encoder *encoder)
>  		return PTR_ERR(psr);
>  
>  	mutex_lock(&psr->lock);
> -	psr->active = true;
> +	--psr->inhibit_count;

Maybe some WARN on negative value?
With doc fixes:
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>

 --
Regards
Andrzej

> +	if (!psr->inhibit_count)
> +		mod_delayed_work(system_wq, &psr->flush_work,
> +				 PSR_FLUSH_TIMEOUT_MS);
>  	mutex_unlock(&psr->lock);
>  
>  	return 0;
>  }
> -EXPORT_SYMBOL(rockchip_drm_psr_activate);
> +EXPORT_SYMBOL(rockchip_drm_psr_inhibit_put);
>  
>  /**
> - * rockchip_drm_psr_deactivate - deactivate PSR on the given pipe
> + * rockchip_drm_psr_inhibit_get - acquire PSR inhibit on given encoder
>   * @encoder: encoder to obtain the PSR encoder
>   *
> + * Increments PSR inhibit count on given encoder. This function guarantees
> + * that after it returns PSR is turned off on given encoder and no PSR-related
> + * hardware state change occurs at least until a matching call to
> + * rockchip_drm_psr_inhibit_put() is done.
> + *
>   * Returns:
>   * Zero on success, negative errno on failure.
>   */
> -int rockchip_drm_psr_deactivate(struct drm_encoder *encoder)
> +int rockchip_drm_psr_inhibit_get(struct drm_encoder *encoder)
>  {
>  	struct psr_drv *psr = find_psr_by_encoder(encoder);
>  
> @@ -137,15 +150,15 @@ int rockchip_drm_psr_deactivate(struct drm_encoder *encoder)
>  		return PTR_ERR(psr);
>  
>  	mutex_lock(&psr->lock);
> -	psr->active = false;
> -	psr->enabled = false;
> +	psr_set_state_locked(psr, false);
> +	++psr->inhibit_count;
>  	mutex_unlock(&psr->lock);
>  	cancel_delayed_work_sync(&psr->flush_work);
>  	cancel_work_sync(&psr->disable_work);
>  
>  	return 0;
>  }
> -EXPORT_SYMBOL(rockchip_drm_psr_deactivate);
> +EXPORT_SYMBOL(rockchip_drm_psr_inhibit_get);
>  
>  static void rockchip_drm_do_flush(struct psr_drv *psr)
>  {
> @@ -301,6 +314,11 @@ static const struct input_device_id psr_ids[] = {
>   * @encoder: encoder that obtain the PSR function
>   * @psr_set: call back to set PSR state
>   *
> + * The function returns with PSR inhibit counter initialized with one
> + * and the caller (typically encoder driver) needs to call
> + * rockchip_drm_psr_inhibit_put() when it becomes ready to accept PSR
> + * enable request.
> + *
>   * Returns:
>   * Zero on success, negative errno on failure.
>   */
> @@ -322,7 +340,7 @@ int rockchip_drm_psr_register(struct drm_encoder *encoder,
>  	INIT_WORK(&psr->disable_work, psr_disable_handler);
>  	mutex_init(&psr->lock);
>  
> -	psr->active = false;
> +	psr->inhibit_count = 1;
>  	psr->enabled = false;
>  	psr->encoder = encoder;
>  	psr->set = psr_set;
> @@ -362,6 +380,11 @@ EXPORT_SYMBOL(rockchip_drm_psr_register);
>   * @encoder: encoder that obtain the PSR function
>   * @psr_set: call back to set PSR state
>   *
> + * It is expected that the PSR inhibit counter is 1 when this function is
> + * called, which corresponds to a state when related encoder has been
> + * disconnected from any CRTCs and its driver called
> + * rockchip_drm_psr_inhibit_get() to stop the PSR logic.
> + *
>   * Returns:
>   * Zero on success, negative errno on failure.
>   */
> @@ -373,10 +396,14 @@ void rockchip_drm_psr_unregister(struct drm_encoder *encoder)
>  	mutex_lock(&drm_drv->psr_list_lock);
>  	list_for_each_entry_safe(psr, n, &drm_drv->psr_list, list) {
>  		if (psr->encoder == encoder) {
> -			input_unregister_handler(&psr->input_handler);
> -			cancel_delayed_work_sync(&psr->flush_work);
> -			cancel_work_sync(&psr->disable_work);
> +			/*
> +			 * Any other value would mean that the encoder
> +			 * is still in use.
> +			 */
> +			WARN_ON(psr->inhibit_count != 1);
> +
>  			list_del(&psr->list);
> +			input_unregister_handler(&psr->input_handler);
>  			kfree(psr->input_handler.name);
>  			kfree(psr);
>  		}
> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_psr.h b/drivers/gpu/drm/rockchip/rockchip_drm_psr.h
> index 06537ee27565..40e026c14168 100644
> --- a/drivers/gpu/drm/rockchip/rockchip_drm_psr.h
> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_psr.h
> @@ -18,8 +18,8 @@
>  void rockchip_drm_psr_flush_all(struct drm_device *dev);
>  int rockchip_drm_psr_flush(struct drm_crtc *crtc);
>  
> -int rockchip_drm_psr_activate(struct drm_encoder *encoder);
> -int rockchip_drm_psr_deactivate(struct drm_encoder *encoder);
> +int rockchip_drm_psr_inhibit_put(struct drm_encoder *encoder);
> +int rockchip_drm_psr_inhibit_get(struct drm_encoder *encoder);
>  
>  int rockchip_drm_psr_register(struct drm_encoder *encoder,
>  			int (*psr_set)(struct drm_encoder *, bool enable));