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

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Mon, Feb 05, 2018 at 01:59:05PM +0100, Maarten Lankhorst wrote:
> Op 02-02-18 om 15:46 schreef Ville Syrjälä:
> > 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>
> Yeah, changed it and pushed, thanks for the suggestion. :)
> > 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.
> It could, but it would use 100% of cpu on older kernels that don't support poll(), if that's not a problem we could do it. :)

Maybe we can probe for poll support when we create the pipe_crc object?

-- 
Ville Syrjälä
Intel OTC
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