| Message ID | 9035cddc289cc58a41d6122a10a17e5d27c6fc0f.1357903446.git.hans.verkuil@cisco.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
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@cisco.com> > > The documentation of the error_idx field was incomplete and confusing. > This patch improves it. > > Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com> > --- > .../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 :-) > +step takes place: this checks if all controls in the list are all valid s/all valid/valid/ ? > +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> > + > +<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>
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@cisco.com> > > > > The documentation of the error_idx field was incomplete and confusing. > > This patch improves it. > > > > Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com> > > --- > > .../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@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Hi Hans, On Friday 11 January 2013 13:22:08 Hans Verkuil wrote: > 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@cisco.com> > > > > > > The documentation of the error_idx field was incomplete and confusing. > > > This patch improves it. > > > > > > Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com> > > > --- > > > > > > .../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." Sounds very good to me. With all those changes, Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
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 step +takes place: this checks if all controls in the list are all valid 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> + +<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>