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

[Maarten Lankhorst <maarten.lankhorst@linux.intel.com>]

Op 05-02-18 om 15:16 schreef Ville Syrjälä:
> 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?
>
I fear that will make a mess since you would need to support the fallback path anyway. I think blindly touching the fd with fcntl is better. :)

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