Re: [PATCH] drm/crc: Add support for polling on the data fd.

From: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
To: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org
Subject: Re: [PATCH] drm/crc: Add support for polling on the data fd.
Date: Fri, 2 Feb 2018 16:46:33 +0200	[thread overview]
Message-ID: <20180202144633.GZ5453@intel.com> (raw)
In-Reply-To: <20180202142743.68527-1-maarten.lankhorst@linux.intel.com>

On Fri, Feb 02, 2018 at 03:27:43PM +0100, Maarten Lankhorst wrote:
> This will make it possible for userspace to know whether reading
> will block, without blocking on the fd. This makes it possible to
> drain all queued CRC's in blocking mode, without having to reopen
> the fd.
> 
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> ---
>  drivers/gpu/drm/drm_debugfs_crc.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_debugfs_crc.c b/drivers/gpu/drm/drm_debugfs_crc.c
> index 9dd879589a2c..8af1a74ec64d 100644
> --- a/drivers/gpu/drm/drm_debugfs_crc.c
> +++ b/drivers/gpu/drm/drm_debugfs_crc.c
> @@ -307,10 +307,29 @@ static ssize_t crtc_crc_read(struct file *filep, char __user *user_buf,
>  	return LINE_LEN(crc->values_cnt);
>  }
>  
> +static unsigned int crtc_crc_poll(struct file *file, poll_table *wait)
> +{
> +	struct drm_crtc *crtc = file->f_inode->i_private;
> +	struct drm_crtc_crc *crc = &crtc->crc;
> +	unsigned ret;
> +
> +	poll_wait(file, &crc->wq, wait);
> +
> +	spin_lock_irq(&crc->lock);
> +	if (crc->source && crtc_crc_data_count(crc))
> +		ret = POLLIN;

Most places seem to also set POLLRDNORM. Maybe we should do it as well?

Apart from that this seems good to me.
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Could replace the usleep() loop in igt read_one_crc() with
poll/select() I suppose? Either that or we should switch between
blocking and nonblocking dynamically.

> +	else
> +		ret = 0;
> +	spin_unlock_irq(&crc->lock);
> +
> +	return ret;
> +}
> +
>  static const struct file_operations drm_crtc_crc_data_fops = {
>  	.owner = THIS_MODULE,
>  	.open = crtc_crc_open,
>  	.read = crtc_crc_read,
> +	.poll = crtc_crc_poll,
>  	.release = crtc_crc_release,
>  };
>  
> -- 
> 2.15.1
> 
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> Intel-gfx@lists.freedesktop.org
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-- 
Ville Syrjälä
Intel OTC
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