Re: [PATCH 01/13] acpi: utils: Cleanup acpi_dev_match_cb

[Suzuki K Poulose]

Hi Rafael,

On 06/06/2019 10:14, Rafael J. Wysocki wrote:
> On Wed, Jun 5, 2019 at 5:14 PM Suzuki K Poulose <suzuki.poulose@xxxxxxx> wrote:
> > acpi_dev_match_cb match function modifies the "data" argument
> > to pass on a result which could be easily deduced from the result
> > of the bus_find_device() call at the caller site. Clean this
> > up in preparation to convert the "match" argument for bus_find_device
> > to accept a "const" data pointer, similar to class_find_device. This
> > would allow consolidating the match routines for these two APIs.
>
> This changelog can be improved IMO.

I agree. Will update it.

> In fact, the final goal here is to pass (const void *) as the second
> argument to acpi_dev_match_cb() (which you could do right away in this
> patch if I'm not mistaken) which is because you want to modify the
> prototype of bus_find_device().
>
> So why don't you write something like this in the changelog:
>
> "The prototype of bus_find_device() will be unified with that of
> class_find_device() subsequently, but for this purpose the callback
> functions passed to it need to take (const void *) as the second
> argument.  Consequently, they cannot modify the memory pointed to by
> that argument which currently is not the case for acpi_dev_match_cb().
> However, acpi_dev_match_cb() really need not modify the "match" object
> passed to it, because acpi_dev_get_first_match_dev() which uses it via
> bus_find_device() can easily convert the result of bus_find_device()
> into the pointer to return.

Sure.

> For this reason, update acpi_dev_match_cb() to avoid the redundant
> memory updates and change the type of its second argument to (const
> void *)."

We can't do that quite yet, until we unify the prototype of the
bus_find_device().

> > Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx>
> > Cc: Len Brown <lenb@xxxxxxxxxx>
> > Cc: linux-acpi@xxxxxxxxxxxxxxx
> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> > ---
> >   drivers/acpi/utils.c | 7 +------
> >   1 file changed, 1 insertion(+), 6 deletions(-)
> >
> > diff --git a/drivers/acpi/utils.c b/drivers/acpi/utils.c
> > index 7def63a..1391b63 100644
> > --- a/drivers/acpi/utils.c
> > +++ b/drivers/acpi/utils.c
> > @@ -725,8 +725,6 @@ bool acpi_dev_found(const char *hid)
> >   EXPORT_SYMBOL(acpi_dev_found);
> >
> >   struct acpi_dev_match_info {
> > -       const char *dev_name;
> > -       struct acpi_device *adev;
> >          struct acpi_device_id hid[2];
> >          const char *uid;
> >          s64 hrv;
> > @@ -746,9 +744,6 @@ static int acpi_dev_match_cb(struct device *dev, void *data)
>
> And why not to change the type of the second arg to "const void *data" here?

Because, that would conflict with what bus_find_device() expects now. We make
the change only later. Since this change was a bit more intrusive than simply
changing the type of the parameter, I kept it as a preparatory patch.

Thanks for the review !

Suzuki