On Fri January 11 2013 13:13:47 Laurent Pinchart wrote: > Hi Hans, > > Thanks for the patch. This is much better in my opinion, please see below for > two small comments. > > On Friday 11 January 2013 12:26:03 Hans Verkuil wrote: > > From: Hans Verkuil <hans.verkuil@xxxxxxxxx> > > > > The documentation of the error_idx field was incomplete and confusing. > > This patch improves it. > > > > Signed-off-by: Hans Verkuil <hans.verkuil@xxxxxxxxx> > > --- > > .../DocBook/media/v4l/vidioc-g-ext-ctrls.xml | 44 +++++++++++++---- > > 1 file changed, 37 insertions(+), 7 deletions(-) > > > > diff --git a/Documentation/DocBook/media/v4l/vidioc-g-ext-ctrls.xml > > b/Documentation/DocBook/media/v4l/vidioc-g-ext-ctrls.xml index > > 0a4b90f..e9f9735 100644 > > --- a/Documentation/DocBook/media/v4l/vidioc-g-ext-ctrls.xml > > +++ b/Documentation/DocBook/media/v4l/vidioc-g-ext-ctrls.xml > > @@ -199,13 +199,43 @@ also be zero.</entry> > > <row> > > <entry>__u32</entry> > > <entry><structfield>error_idx</structfield></entry> > > - <entry>Set by the driver in case of an error. If it is equal > > -to <structfield>count</structfield>, then no actual changes were made to > > -controls. In other words, the error was not associated with setting a > > -particular control. If it is another value, then only the controls up to > > -<structfield>error_idx-1</structfield> were modified and control > > -<structfield>error_idx</structfield> is the one that caused the error. The > > -<structfield>error_idx</structfield> value is undefined if the ioctl > > -returned 0 (success).</entry> > > + <entry><para>Set by the driver in case of an error. If the error is > > +associated with a particular control, then > > +<structfield>error_idx</structfield> is set to the index of that control. > > +If the error is not related to a specific control, or the pre-validation > > +step failed (see below), then <structfield>error_idx</structfield> is set > > +to <structfield>count</structfield>. The value is undefined if the ioctl > > +returned 0 (success).</para> > > + > > +<para>Before controls are read from/written to hardware a pre-validation > > Maybe s/pre-validation/validation/ through the text ? We have a single > validation step, it feels a bit weird to talk about pre-validation when > there's no further validation :-) OK. > > +step takes place: this checks if all controls in the list are all valid > > s/all valid/valid/ ? Indeed. > > > +controls, if no attempt is made to write to a read-only control or read > > +from a write-only control, and any other up-front checks that can be done > > +without accessing the hardware.</para> How about adding this sentence to the end of the paragraph: "The exact validations done during this step are driver dependent since some checks might require hardware access for some devices, thus making it impossible to do those checks up-front. However, drivers should make a best-effort to do as many up-front checks as possible." Regards, Hans > > + > > +<para>This check is done to avoid leaving the hardware in an inconsistent > > +state due to easy-to-avoid problems. But it leads to another problem: the > > +application needs to know whether an error came from the pre-validation > > +step (meaning that the hardware was not touched) or from an error during > > +the actual reading from/writing to hardware.</para> > > + > > +<para>The, in hindsight quite poor, solution for that is to set > > +<structfield>error_idx</structfield> to <structfield>count</structfield> > > +if the pre-validation failed. This has the unfortunate side-effect that it > > +is not possible to see which control failed the pre-validation. If the > > +pre-validation was successful and the error happened while accessing the > > +hardware, then <structfield>error_idx</structfield> is less than > > +<structfield>count</structfield> and only the controls up to > > +<structfield>error_idx-1</structfield> were read or written correctly, and > > +the state of the remaining controls is undefined.</para> > > + > > +<para>Since <constant>VIDIOC_TRY_EXT_CTRLS</constant> does not access > > +hardware there is also no need to handle the pre-validation step in this > > +special way, so <structfield>error_idx</structfield> will just be set to > > +the control that failed the pre-validation step instead of to > > +<structfield>count</structfield>. This means that if > > +<constant>VIDIOC_S_EXT_CTRLS</constant> fails with > > +<structfield>error_idx</structfield> set to > > +<structfield>count</structfield>, then you can call > > +<constant>VIDIOC_TRY_EXT_CTRLS</constant> to try to discover the actual > > +control that failed the pre-validation step. Unfortunately, there is no > > +<constant>TRY</constant> equivalent for > > +<constant>VIDIOC_G_EXT_CTRLS</constant>. </para></entry> > > </row> > > <row> > > <entry>__u32</entry> > -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
