Re: [PATCH] fsi: core: Fix legacy minor numbering

[Eddie James]

On 5/30/23 20:54, Joel Stanley wrote:
> On Thu, 13 Apr 2023 at 16:24, Eddie James <eajames@xxxxxxxxxxxxx> wrote:
> > FSI reserves the first 64 minor numbers for the legacy numbering
> > based on the chip id. However the legacy number shifts the chip
> > id too much, resulting in overlap between legacy and non-legacy
> > numbers. Reduce the chip id bit shift since the type field only
> > takes 2 bits.
> I don't know much about the legacy numbering. Was that something we
> used before the device tree descriptions were in place? Do we still
> need it if we have updated device trees?


Its a way to number the devices based on the "chip id", which came from 
the device tree anyway. Now with the aliasing patch we could do away 
with it I believe, but we would need to update older system device trees 
(and scom devices on p10) to not break stuff.

> > Signed-off-by: Eddie James <eajames@xxxxxxxxxxxxx>
> > ---
> >   drivers/fsi/fsi-core.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/fsi/fsi-core.c b/drivers/fsi/fsi-core.c
> > index 0b927c9f4267..b9f410170655 100644
> > --- a/drivers/fsi/fsi-core.c
> > +++ b/drivers/fsi/fsi-core.c
> > @@ -950,7 +950,7 @@ static int __fsi_get_new_minor(struct fsi_slave *slave, enum fsi_dev_type type,
> >          /* Check if we qualify for legacy numbering */
> >          if (cid >= 0 && cid < 16 && type < 4) {
> >                  /* Try reserving the legacy number */
> Would it help to put some of your commit message info in this comment,
> so we know what the magic shift is doing?


Sure thing.

Thanks,

Eddie


> > -               id = (cid << 4) | type;
> > +               id = (cid << 2) | type;
> >                  id = ida_simple_get(&fsi_minor_ida, id, id + 1, GFP_KERNEL);
> >                  if (id >= 0) {
> >                          *out_index = fsi_adjust_index(cid);
> > --
> > 2.31.1