Hi Hans,
On Tue, Sep 19, 2017 at 11:21:50AM +0200, Hans Verkuil wrote:
> On 09/19/17 10:45, Sakari Ailus wrote:
> > Hi Hans,
> >
> > Thank you for the review.
> >
> > On Tue, Sep 19, 2017 at 10:31:41AM +0200, Hans Verkuil wrote:
> >> Hi Sakari,
> >>
> >> I'm slowly starting to understand this. The example helped a lot. But I still have
> >> some questions, see below.
> >>
> >> On 09/15/2017 04:17 PM, Sakari Ailus wrote:
> >>> v4l2_fwnode_reference_parse_int_prop() will find an fwnode such that under
> >>> the device's own fwnode, it will follow child fwnodes with the given
> >>> property-value pair and return the resulting fwnode.
> >>
> >> I think both the subject, commit log, function comment and function name should
> >> reflect the fact that this function is for an ACPI reference.
> >>
> >> It's only called for ACPI (from patch 19):
> >>
> >> + if (props[i].props && is_acpi_node(dev_fwnode(dev)))
> >> + ret = v4l2_fwnode_reference_parse_int_props(
> >>
> >> So renaming it to v4l2_fwnode_acpi_reference_parse_int_props or something similar
> >> would clarify this fact.
> >
> > I don't think we'll see many like this one. I presume we won't use it on DT
> > albeit there are no direct references to ACPI in the code itself.
> >
> > How about v4l2_fwnode_parse_acpi_reference (+ "s" for the one below)?
>
> Sounds good.
>
> >
> >>
> >>>
> >>> Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
> >>> ---
> >>> drivers/media/v4l2-core/v4l2-fwnode.c | 201 ++++++++++++++++++++++++++++++++++
> >>> 1 file changed, 201 insertions(+)
> >>>
> >>> diff --git a/drivers/media/v4l2-core/v4l2-fwnode.c b/drivers/media/v4l2-core/v4l2-fwnode.c
> >>> index 65e84ea1cc35..968a345a288f 100644
> >>> --- a/drivers/media/v4l2-core/v4l2-fwnode.c
> >>> +++ b/drivers/media/v4l2-core/v4l2-fwnode.c
> >>> @@ -567,6 +567,207 @@ static int v4l2_fwnode_reference_parse(
> >>> return ret;
> >>> }
> >>>
> >>> +/*
> >>> + * v4l2_fwnode_reference_get_int_prop - parse a reference with integer
> >>> + * arguments
> >>> + * @dev: struct device pointer
> >>> + * @notifier: notifier for @dev
> >>> + * @prop: the name of the property
> >>> + * @index: the index of the reference to get
> >>> + * @props: the array of integer property names
> >>> + * @nprops: the number of integer property names in @nprops
> >>
> >> You mean 'in @props'?
> >
> > Yes, I'll fix that.
> >
> >>
> >> One thing that is not clear to me is when you would use an nprops value > 1.
> >> What's the use-case for that? It only makes sense (I think) if you would have
> >> property names that are all aliases of one another.
> >
> > There may be several flash LEDs related to a sensor. That's the use case,
> > for instance.
>
> I think it would be helpful if the example shows two LEDs related to a
> sensor. Part of the problem I have in understanding this code is that I
> have zero experience with ACPI (and that is probably true for most other
> developers), so I don't know how this is encoded. With a good example it
> is much easier to understand.
I'm a bit at loss here. Are you happy with the example below, or do you
think something is missing in the documentation here.
>
> >
> >>
> >>> + *
> >>> + * Find fwnodes referred to by a property @prop, then under that
> >>> + * iteratively, @nprops times, follow each child node which has a
> >>> + * property in @props array at a given child index the value of which
> >>> + * matches the integer argument at an index.
> >>> + *
> >>> + * For example, if this function was called with arguments and values
> >>> + * @dev corresponding to device "SEN", @prop == "flash-leds", @index
> >>> + * == 1, @props == { "led" }, @nprops == 1, with the ASL snippet below
> >>> + * it would return the node marked with THISONE. The @dev argument in
> >>> + * the ASL below.
> >>
> >> That last sentence about the @dev seems incomplete. I'm not sure what is
> >> meant by it.
> >
> > I think it was meant to convey some information but it got added to the
> > previous sentence. I'll remove it.
> >
> >>
> >>> + *
> >>> + * Device (LED)
> >>> + * {
> >>> + * Name (_DSD, Package () {
> >>> + * ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"),
> >>> + * Package () {
> >>> + * Package () { "led0", "LED0" },
> >>> + * Package () { "led1", "LED1" },
> >>> + * }
> >>> + * })
> >>> + * Name (LED0, Package () {
> >>> + * ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
> >>> + * Package () {
> >>> + * Package () { "led", 0 },
> >>> + * }
> >>> + * })
> >>> + * Name (LED1, Package () {
> >>> + * // THISONE
> >>> + * ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
> >>> + * Package () {
> >>> + * Package () { "led", 1 },
> >>> + * }
> >>> + * })
> >>> + * }
> >>> + *
> >>> + * Device (SEN)
> >>> + * {
> >>> + * Name (_DSD, Package () {
> >>> + * ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
> >>> + * Package () {
> >>> + * Package () {
> >>> + * "flash-leds",
> >>> + * Package () { ^LED, 0, ^LED, 1 },
> >>> + * }
> >>> + * }
> >>> + * })
> >>> + * }
> >>> + *
> >>> + * where
> >>> + *
> >>> + * LED LED driver device
> >>> + * LED0 First LED
> >>> + * LED1 Second LED
> >>> + * SEN Camera sensor device (or another device the LED is
> >>> + * related to)
> >>> + *
> >>> + * Return: 0 on success
> >>> + * -ENOENT if no entries (or the property itself) were found
> >>> + * -EINVAL if property parsing otherwise failed
> >>> + * -ENOMEM if memory allocation failed
> >>> + */
> >>> +static struct fwnode_handle *v4l2_fwnode_reference_get_int_prop(
> >>> + struct fwnode_handle *fwnode, const char *prop, unsigned int index,
> >>> + const char **props, unsigned int nprops)
> >>> +{
> >>> + struct fwnode_reference_args fwnode_args;
> >>> + unsigned int *args = fwnode_args.args;
> >>> + struct fwnode_handle *child;
> >>> + int ret;
> >>> +
> >>> + /*
> >>> + * Obtain remote fwnode as well as the integer arguments.
> >>> + *
> >>> + * Note that right now both -ENODATA and -ENOENT may signal
> >>> + * out-of-bounds access. Return -ENOENT in that case.
> >>> + */
> >>> + ret = fwnode_property_get_reference_args(fwnode, prop, NULL, nprops,
> >>> + index, &fwnode_args);
> >>> + if (ret)
> >>> + return ERR_PTR(ret == -ENODATA ? -ENOENT : ret);
> >>> +
> >>> + /*
> >>> + * Find a node in the tree under the referred fwnode corresponding the
> >>> + * integer arguments.
> >>> + */
> >>> + fwnode = fwnode_args.fwnode;
> >>
> >> So given the example above, fwnode would point to the LED device?
> >>
> >> If correct, then mention that in the comment.
> >
> > It could be a LED driver device, but it could be something else as well.
> > Like a lens VCM, depending on the property being parsed. That's why I
> > didn't put it in the comments. But this is a device node, not a
> > hierarchical data extension node, for instance. That's what I think I
> > should add.
>
> I think that will help.
Agreed.
Yeah, in DT all fwnodes are DT nodes but in ACPI some are device nodes and
others hierarchical data extension nodes. Oh well...
>
> >
> >>
> >>> + while (nprops--) {
> >>> + u32 val;
> >>> +
> >>> + /* Loop over all child nodes under fwnode. */
> >>
> >> And here you check if the LED device has child nodes that have a *props
> >> property with a value matching the index.
> >>
> >> So given the example above it is looking for a child with property "led"
> >> and value 1.
> >>
> >> It's useful if that is mentioned in the comment as well.
> >
> > But should I? This isn't specific to LEDs.
>
> Ignore this comment for now. I'll take another look when I see v14.
--
Regards,
Sakari Ailus
sakari.ailus@xxxxxxxxxxxxxxx
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