Re: [PATCH v3 3/5] drm/dp: add helpers for capture of frame CRCs

[Sean Paul]

On Fri, Jan 6, 2017 at 9:30 AM, Tomeu Vizoso <tomeu.vizoso@xxxxxxxxxxxxx> wrote:
> Adds helpers for starting and stopping capture of frame CRCs through the
> DPCD. When capture is on, a worker waits for vblanks and retrieves the
> frame CRC to put it in the queue on the CRTC that is using the
> eDP connector, so it's passed to userspace.
>
> v2: Reuse drm_crtc_wait_one_vblank
>     Update locking, as drm_crtc_add_crc_entry now takes the lock
>
> v3: Don't call wake_up_interruptible directly, that's now done in
>     drm_crtc_add_crc_entry.
>
> Signed-off-by: Tomeu Vizoso <tomeu.vizoso@xxxxxxxxxxxxx>
> ---
>
>  drivers/gpu/drm/drm_dp_helper.c | 118 ++++++++++++++++++++++++++++++++++++++++
>  include/drm/drm_dp_helper.h     |   7 +++
>  2 files changed, 125 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index 3e6fe82c6d64..e531f1317268 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -981,6 +981,74 @@ static const struct i2c_lock_operations drm_dp_i2c_lock_ops = {
>         .unlock_bus = unlock_bus,
>  };
>
> +static int drm_dp_aux_get_crc(struct drm_dp_aux *aux, u8 *crc)
> +{
> +       u8 buf, count;
> +       int ret;
> +
> +       ret = drm_dp_dpcd_readb(aux, DP_TEST_SINK, &buf);
> +       if (ret < 0)
> +               return ret;
> +
> +       WARN_ON(!(buf & DP_TEST_SINK_START));
> +
> +       ret = drm_dp_dpcd_readb(aux, DP_TEST_SINK_MISC, &buf);
> +       if (ret < 0)
> +               return ret;
> +
> +       count = buf & DP_TEST_COUNT_MASK;
> +       if (count == aux->crc_count)
> +               return -EAGAIN; /* No CRC yet */
> +
> +       aux->crc_count = count;
> +
> +       /* At DP_TEST_CRC_R_CR, there's 6 bytes containing CRC data, 2 bytes
> +        * per component (RGB or CrYCb).

nit: doesn't conform to CodingStyle

> +        */
> +       ret = drm_dp_dpcd_read(aux, DP_TEST_CRC_R_CR, crc, 6);
> +       if (ret < 0)
> +               return ret;
> +
> +       return 0;
> +}
> +
> +static void drm_dp_aux_crc_work(struct work_struct *work)
> +{
> +       struct drm_dp_aux *aux = container_of(work, struct drm_dp_aux,
> +                                             crc_work);
> +       struct drm_crtc *crtc;
> +       u8 crc_bytes[6];
> +       uint32_t crcs[3];
> +       int ret;
> +
> +       if (WARN_ON(!aux->connector))
> +               return;
> +
> +       crtc = aux->connector->state->crtc;
> +       while (crtc->crc.opened) {
> +               drm_crtc_wait_one_vblank(crtc);
> +               if (!crtc->crc.opened)
> +                       break;
> +
> +               ret = drm_dp_aux_get_crc(aux, crc_bytes);
> +               if (ret == -EAGAIN) {
> +                       usleep_range(1000, 2000);
> +                       ret = drm_dp_aux_get_crc(aux, crc_bytes);
> +               }
> +
> +               if (ret) {
> +                       DRM_DEBUG_KMS("Failed to get a CRC even after retrying: %d\n",
> +                                     ret);
> +                       continue;
> +               }

I think it'd be better to restructure this to only call
drm_dp_aux_get_crc in one place (and differentiate between EAGAIN and
other failures):

bool retry = false;
while (...) {
        ...

        ret = drm_dp_aux_get_crc(aux, crc_bytes);
        if (ret == -EAGAIN) {
                if (retry)
                        DRM_DEBUG_KMS("Get CRC failed after retrying: %d\n",
                                      ret);
                retry = !retry;
                usleep_range(1000, 2000);
                continue;
        }

        retry = false;
        if (!ret) {
                crcs[0] = crc_bytes[0] | crc_bytes[1] << 8;
                crcs[1] = crc_bytes[2] | crc_bytes[3] << 8;
                crcs[2] = crc_bytes[4] | crc_bytes[5] << 8;
                ret = drm_crtc_add_crc_entry(crtc, false, 0, crcs);
                if (ret)
                        DRM_DEBUG_KMS("Failed to add crc entry %d\n", ret);
        } else {
                DRM_DEBUG_KMS("Get CRC failed: %d\n", ret);
        }
}

> +
> +               crcs[0] = crc_bytes[0] | crc_bytes[1] << 8;
> +               crcs[1] = crc_bytes[2] | crc_bytes[3] << 8;
> +               crcs[2] = crc_bytes[4] | crc_bytes[5] << 8;
> +               ret = drm_crtc_add_crc_entry(crtc, false, 0, crcs);
> +       }
> +}
> +
>  /**
>   * drm_dp_aux_init() - minimally initialise an aux channel
>   * @aux: DisplayPort AUX channel
> @@ -993,6 +1061,7 @@ static const struct i2c_lock_operations drm_dp_i2c_lock_ops = {
>  void drm_dp_aux_init(struct drm_dp_aux *aux)
>  {
>         mutex_init(&aux->hw_mutex);
> +       INIT_WORK(&aux->crc_work, drm_dp_aux_crc_work);
>
>         aux->ddc.algo = &drm_dp_i2c_algo;
>         aux->ddc.algo_data = aux;
> @@ -1081,3 +1150,52 @@ int drm_dp_psr_setup_time(const u8 psr_cap[EDP_PSR_RECEIVER_CAP_SIZE])
>  EXPORT_SYMBOL(drm_dp_psr_setup_time);
>
>  #undef PSR_SETUP_TIME
> +
> +/**
> + * drm_dp_start_crc() - start capture of frame CRCs
> + * @aux: DisplayPort AUX channel
> + *
> + * Returns 0 on success or a negative error code on failure.
> + */
> +int drm_dp_start_crc(struct drm_dp_aux *aux)
> +{
> +       u8 buf;
> +       int ret;
> +
> +       ret = drm_dp_dpcd_readb(aux, DP_TEST_SINK, &buf);
> +       if (ret < 0)
> +               return ret;
> +
> +       ret = drm_dp_dpcd_writeb(aux, DP_TEST_SINK, buf | DP_TEST_SINK_START);
> +       if (ret < 0)
> +               return ret;
> +
> +       aux->crc_count = 0;
> +       schedule_work(&aux->crc_work);
> +
> +       return 0;
> +}
> +EXPORT_SYMBOL(drm_dp_start_crc);
> +
> +/**
> + * drm_dp_stop_crc() - stop capture of frame CRCs
> + * @aux: DisplayPort AUX channel
> + *
> + * Returns 0 on success or a negative error code on failure.
> + */
> +int drm_dp_stop_crc(struct drm_dp_aux *aux)
> +{
> +       u8 buf;
> +       int ret;
> +
> +       ret = drm_dp_dpcd_readb(aux, DP_TEST_SINK, &buf);
> +       if (ret < 0)
> +               return ret;
> +
> +       ret = drm_dp_dpcd_writeb(aux, DP_TEST_SINK, buf & ~DP_TEST_SINK_START);
> +       if (ret < 0)
> +               return ret;
> +

Can we flush the worker here to head off any races?


> +       return 0;
> +}
> +EXPORT_SYMBOL(drm_dp_stop_crc);
> diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> index 4fa77b434594..276e1ecd947b 100644
> --- a/include/drm/drm_dp_helper.h
> +++ b/include/drm/drm_dp_helper.h
> @@ -723,6 +723,8 @@ struct drm_dp_aux_msg {
>   * @dev: pointer to struct device that is the parent for this AUX channel
>   * @connector: backpointer to connector that uses this AUX channel
>   * @hw_mutex: internal mutex used for locking transfers
> + * @crc_work: worker that captures CRCs for each frame
> + * @crc_count: counter of captured frame CRCs
>   * @transfer: transfers a message representing a single AUX transaction
>   *
>   * The .dev field should be set to a pointer to the device that implements
> @@ -760,6 +762,8 @@ struct drm_dp_aux {
>         struct device *dev;
>         struct drm_connector *connector;
>         struct mutex hw_mutex;
> +       struct work_struct crc_work;
> +       u8 crc_count;
>         ssize_t (*transfer)(struct drm_dp_aux *aux,
>                             struct drm_dp_aux_msg *msg);
>         /**
> @@ -838,4 +842,7 @@ void drm_dp_aux_init(struct drm_dp_aux *aux);
>  int drm_dp_aux_register(struct drm_dp_aux *aux);
>  void drm_dp_aux_unregister(struct drm_dp_aux *aux);
>
> +int drm_dp_start_crc(struct drm_dp_aux *aux);
> +int drm_dp_stop_crc(struct drm_dp_aux *aux);
> +
>  #endif /* _DRM_DP_HELPER_H_ */
> --
> 2.9.3
>



-- 
Sean Paul, Software Engineer, Google / Chromium OS