Hi Tomi,
On Mon, Sep 27, 2021 at 11:55:38AM +0300, Tomi Valkeinen wrote:
> On 27/09/2021 03:48, Laurent Pinchart wrote:
> > On Thu, Sep 16, 2021 at 04:24:19PM +0300, Tomi Valkeinen wrote:
> >> On 16/09/2021 16:07, Jacopo Mondi wrote:
> >>
> >>> Also note that operations like s_stream do not take a state as
> >>> parameter. The driver has to fetch it from the subdev anyway
> >>> (this in reply to the idea of having the active state as parameter vs
> >>> retrieving it from the subdev if ACTIVE)
> >>>
> >>> While porting the R-Car drivers on top of this series I found myself
> >>> in the need to (in the s_stream call chain)
> >>>
> >>> static int rcsi2_start_receiver(struct rcar_csi2 *priv)
> >>> {
> >>> const struct v4l2_subdev_state *state = priv->subdev.state;
> >>> const struct v4l2_subdev_stream_configs *configs = &state->stream_configs;
> >>>
> >>> ...
> >>>
> >>> /*
> >>> * Configure field handling inspecting the formats of the
> >>> * single sink pad streams.
> >>> */
> >>> for (i = 0; i < configs->num_configs; ++i) {
> >>> const struct v4l2_subdev_stream_config *config = configs->configs;
> >>> if (config->pad != RCAR_CSI2_SINK)
> >>> continue;
> >>>
> >>> if (config->fmt.field != V4L2_FIELD_ALTERNATE)
> >>> continue;
> >>>
> >>> fld |= FLD_DET_SEL(1);
> >>> fld |= FLD_FLD_EN(config->stream);
> >>>
> >>> /* PAL vs NTSC. */
> >>> if (config->fmt.height == 240)
> >>> fld |= FLD_FLD_NUM(0);
> >>> else
> >>> fld |= FLD_FLD_NUM(1);
> >>> }
> >>>
> >>> ...
> >>>
> >>> }
> >>>
> >>> Am I doing it wrong, or is this a case for the subdev to have to
> >>> directly access sd->state ?
> >>
> >> In s_stream path you should:
> >>
> >> state = v4l2_subdev_lock_active_state(sd);
> >>
> >> <do the work with the state>
> >>
> >> v4l2_subdev_unlock_state(state);
> >>
> >> If you already have the state, e.g. in set_fmt:
> >>
> >> state = v4l2_subdev_validate_and_lock_state(sd, state);
> >>
> >> <do the work with the state>
> >>
> >> v4l2_subdev_unlock_state(state);
> >>
> >> Accessing the stream_configs directly is fine but not that nice. I did
> >> think about some helpers, perhaps for_each_stream_config(), but I didn't
> >> add that as I didn't have the need.
> >>
> >> There's v4l2_state_get_stream_format() which can be used in many cases,
> >> but we probably need something else if you need to iterate over all the
> >> configs.
> >
> > I really like forcing drivers to call functions that will lock the
> > state, at least until we can move the locks to the core (if ever). We
> > should move the fields of v4l2_subdev that drivers are not supposed to
> > access directly under a big PRIVATE comment.
>
> Can you clarify what you mean here? Did you mean you like functions that
> will _check_ the lock? Or did you just mean that you like
> v4l2_subdev_lock_state() better than mutex_lock(state->lock)?
I like v4l2_subdev_lock_state().
> Well, in any case, I think my series does both =). I can add the private
> comment to subdev. In fact, at one time I did not have sd->state, but
> sd->_state, just to make sure no one accesses it.
I half recall there was a gcc attribute to mark private fields in a
structure, which then generates a warning if those fields are accessed
by a function that doesn't have another special attribute. Or maybe I
was dreaming :-)
--
Regards,
Laurent Pinchart
