Re: [PATCH] media: i2c: ccs: Fix link frequency control range update

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

On Sat, Jun 29, 2024 at 11:34:11AM +0000, Sakari Ailus wrote:
> On Sat, Jun 29, 2024 at 01:52:22PM +0300, Laurent Pinchart wrote:
> > On Sat, Jun 29, 2024 at 08:56:09AM +0000, Sakari Ailus wrote:
> > > Hi Laurent,
> > > 
> > > Thanks for the patch.
> > > 
> > > On Sat, Jun 29, 2024 at 12:26:03AM +0300, Laurent Pinchart wrote:
> > > > When updating the link frequency control range in response to a format
> > > > change, the minimum value passed to the __v4l2_ctrl_modify_range()
> > > > function is hardcoded to 0, while there's no guarantee that the first
> > > > link frequency in the menu is valid for the selected format. Fix it by
> > > > getting using the index of the first bit set in the valid link
> > > > frequencies mask.
> > > 
> > > Is this a problem? The bitmask does tell which ones are valid, doesn't it?
> > 
> > I noticed that the new range wasn't applied in my sensor driver when the
> > minimum was set to 0 and the mask didn't include that bit. However,
> > that's because I had the default value wrong, which caused
> > __v4l2_ctrl_modify_range() to error out. I thought the same applied to
> > the minimum, but that doesn't seem to be the case. Isn't it still
> > clearer to set the correct minimum, given that it is already computed
> > anyway, to be used as a default value ?
> 
> I guess from user space point of view this could be helpful, yes. I'm fine
> with changing this.

Another option would be for the control framework to adjust the minimum
and maximum based on the mask.

> > > The minimum value will also be zero after control initialisation before
> > > this function gets called. This should be also taken into account.
> > > 
> > > > Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > > > ---
> > > > I noticed this issue in the CCS driver while working on a different
> > > > sensor driver. I haven't tested this patch.
> > > > ---
> > > >  drivers/media/i2c/ccs/ccs-core.c | 12 ++++++++----
> > > >  1 file changed, 8 insertions(+), 4 deletions(-)
> > > > 
> > > > diff --git a/drivers/media/i2c/ccs/ccs-core.c b/drivers/media/i2c/ccs/ccs-core.c
> > > > index e1ae0f9fad43..5257dc4912ae 100644
> > > > --- a/drivers/media/i2c/ccs/ccs-core.c
> > > > +++ b/drivers/media/i2c/ccs/ccs-core.c
> > > > @@ -2143,6 +2143,7 @@ static int ccs_set_format_source(struct v4l2_subdev *subdev,
> > > >  		*old_csi_format = sensor->csi_format;
> > > >  	unsigned long *valid_link_freqs;
> > > >  	u32 code = fmt->format.code;
> > > > +	unsigned int min, max;
> > > >  	unsigned int i;
> > > >  	int rval;
> > > >  
> > > > @@ -2179,10 +2180,13 @@ static int ccs_set_format_source(struct v4l2_subdev *subdev,
> > > >  		&sensor->valid_link_freqs[sensor->csi_format->compressed
> > > >  					  - sensor->compressed_min_bpp];
> > > >  
> > > > -	__v4l2_ctrl_modify_range(
> > > > -		sensor->link_freq, 0,
> > > > -		__fls(*valid_link_freqs), ~*valid_link_freqs,
> > > > -		__ffs(*valid_link_freqs));
> > > > +	min = __ffs(*valid_link_freqs);
> > > > +	man = __fls(*valid_link_freqs);
> > > > +
> > > > +	ret = __v4l2_ctrl_modify_range(sensor->link_freq, min, max,
> > > > +				       ~*valid_link_freqs, min);
> > > 
> > > As this doesn't effect any actual change the applying of which could fail,
> > > you'd have to have an issue with the argument values themselves. I wouldn't
> > > add a check here. Although if you do, the sensor configuration should be
> > > returned to the state before the call which would probably be worth a new
> > > patch.
> > 
> > The lack of a similar check caused my driver to silently keep the
> > current range, and it took me a while to debug that. I however agree
> > that, if the arguments are right, the check isn't needed. Maybe it can
> > be dropped, as the arguments are correct.
> 
> Alternatively there should be a dev_warn(), too, that this is a driver bug.

Do you think we should add the warning to the __v4l2_ctrl_modify_range()
function, or are there use cases where it could fail during normal
operation ?

> > > > +	if (ret)
> > > > +		return ret;
> > > >  
> > > >  	return ccs_pll_update(sensor);
> > > >  }
> > > > 
> > > > base-commit: afcd48134c58d6af45fb3fdb648f1260b20f2326

-- 
Regards,

Laurent Pinchart