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    SubjectRe: [PATCH 02/14] soundwire: Add SoundWire bus type
    On Fri, 20 Oct 2017 17:46:49 +0200,
    Vinod Koul wrote:
    >
    > On Fri, Oct 20, 2017 at 08:59:42AM +0200, Takashi Iwai wrote:
    > > On Fri, 20 Oct 2017 07:11:01 +0200,
    > > Vinod Koul wrote:
    > > >
    > > > On Thu, Oct 19, 2017 at 09:40:06AM +0200, Takashi Iwai wrote:
    > > > > On Thu, 19 Oct 2017 05:03:18 +0200,
    > > > > Vinod Koul wrote:
    > > > > > +
    > > > > > +config SOUNDWIRE_BUS
    > > > > > + tristate
    > > > > > + default SOUNDWIRE
    > > > > > +
    > > > >
    > > > > Does it make sense to be tristate?
    > > > > Since CONFIG_SOUNDWIRE is a bool, the above would be also only either
    > > > > Y or N. If it's Y and others select M, it'll be still Y.
    > > >
    > > > hmmm good point. I think would make sense to make SOUNDWIRE as tristate too,
    > > > just like SOUND :)
    > >
    > > It's one option. Another would be to simply drop the "default" line.
    >
    > Okay good suggestion
    >
    > > > > > + * The match is done by comparing the mfg_id and part_id from the
    > > > > > + * struct sdw_device_id. class_id is unused, as it is a placeholder
    > > > > > + * in MIPI Spec.
    > > > > > + */
    > > > > > +static const struct sdw_device_id *
    > > > > > +sdw_get_device_id(struct sdw_slave *slave, struct sdw_driver *drv)
    > > > > > +{
    > > > > > + const struct sdw_device_id *id = drv->id_table;
    > > > > > +
    > > > > > + while (id && id->mfg_id) {
    > > > > > + if (slave->id.mfg_id == id->mfg_id &&
    > > > > > + slave->id.part_id == id->part_id) {
    > > > >
    > > > > Please indentation properly.
    > > >
    > > > what do you advise?
    > > >
    > > > if (slave->id.mfg_id == id->mfg_id &&
    > > > slave->id.part_id == id->part_id) {
    > > >
    > > > would mean below one is at same indent. Some people use:
    > > >
    > > > if (slave->id.mfg_id == id->mfg_id &&
    > > > slave->id.part_id == id->part_id) {
    > > >
    > > > Is it Documented anywhere...
    > >
    > > This is a matter of taste. The latter is the way Emacs or indent does
    > > as default.
    >
    > okay as vi user I will try to do above :)
    >
    > >
    > > > > > --- a/include/linux/mod_devicetable.h
    > > > > > +++ b/include/linux/mod_devicetable.h
    > > > > > @@ -228,6 +228,13 @@ struct hda_device_id {
    > > > > > unsigned long driver_data;
    > > > > > };
    > > > > >
    > > > > > +struct sdw_device_id {
    > > > > > + __u16 mfg_id;
    > > > > > + __u16 part_id;
    > > > > > + __u8 class_id;
    > > > > > + kernel_ulong_t driver_data;
    > > > >
    > > > > Better to think of alignment.
    > > >
    > > > sorry not quite clear, do you mind elaborating which ones to align?
    > >
    > > kernel_ulong_t may be aligned to 4 or 8 bytes, depending on
    > > architecture, so there can be a hole between class_id and driver_data.
    > > It's not an ABI, so we don't have to care too much, but it's still
    > > something exposed, hence better to be conscious about alignment.
    >
    > ah :) is that why hda is unsigned long :) Btw doesnt that cause compat
    > issues, should we not do something like u64 here?

    Oh, don't take the HD-audio case as a good reference, it's a bad guy
    ;) In the case of hda, the definition isn't really exposed.

    The alignment doesn't matter whether it's unsigned long or
    kernel_ulong_t. It's a generic issue when you define some struct and
    expose it. In a safer side, you can put the enough pad bytes so that
    the long field is aligned in 8 bytes. Or use packed struct. Or you
    can just ignore and let it be so, but aware of the possible holes in
    your code.


    Takashi

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