Re: [PATCH v2 2/2] i2c: designware: Add AMD PSP I2C bus support

[Jan Dąbroś]

pon., 31 sty 2022 o 14:32 Andy Shevchenko
<andriy.shevchenko@xxxxxxxxxxxxxxx> napisał(a):
>
> On Mon, Jan 31, 2022 at 12:56:27PM +0100, Jan Dąbroś wrote:
> > pt., 28 sty 2022 o 16:50 Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> > napisał(a):
> > > On Fri, Jan 28, 2022 at 03:59:40PM +0100, Jan Dąbroś wrote:
> > > > pt., 28 sty 2022 o 15:48 Jan Dabros <jsd@xxxxxxxxxxxx> napisał(a):
>
> ...
>
> > > > > +struct psp_mbox {
> > > > > +       u32 cmd_fields;
> > >
> > > > > +       phys_addr_t i2c_req_addr;
> > >
> > > But phys_addr_t is platform-dependent type. Perhaps you meant to use u64
> > > here
> > > always?
> >
> > Once I remove the "depends on X86_64" I believe this should be left
> > platform-dependent.
>
> If it's a protocol or HW layout, it may not be platform-dependent.

Right you are correct, will keep this as 64bit variable.

>
> > > > > +} __packed;
>
> ...
>
> > > > > +       if (psp_send_cmd(req))
> > >
> > > > > +               return -EIO;
> > >
> > > Why is error code shadowed?
> > >
> >
> > Just as a side note - it wasn't modified in v2 when moving above to
> > psp_send_check_i2c_req(), but let me explain why I have introduced this
> > initially.
> >
> > We have two means of timeouts in the context of this driver:
> > 1. Timeout of internal mailbox, which means we cannot communicate with a
> > PSP for a programmed timeout. This timeout is encountered inside
> > psp_send_cmd().
> > 2. Timeout of i2c arbitration - which means that we can communicate with
> > PSP, but PSP refuses to release i2c bus for too long. This timeout is
> > returned by psp_send_i2c_req() in case of error.
> > (side note: both error conditions are very unlikely to happen at runtime)
> >
> > I wanted to clearly distinguish between these two and thus put all errors
> > around mailbox into "-EIO category", which is actually true.
>
> At very least this code needs more or less the above to be put as a comment.

ACK

>
> ...
>
> > > > > +cleanup:
> > > > > +       mutex_unlock(&psp_i2c_access_mutex);
> > > > > +       return 0;
> > >
> > > Not sure I understand why we ignore all above errors here.
> > >
> >
> > Actually we are not ignoring them, since each error sets "psp_i2c_mbox_fail
> > = true;". This means that if there is any error on x86-PSP interface, we
> > are ignoring i2c-arbitration and just fall back to normal (that is
> > no-quirk) operation.
> >
> > From the i2c-client perspective (who is eventually gathering error code
> > from above) I think we can claim that everything is fine, since bus is
> > granted to it. For developers there is an error message in case some debug
> > will be necessary.
>
> Perhaps needs a comment (sorry, if I overlooked it).

ACK.

>
> ...
>
> > > > > +       if (!dev || !dev->dev)
> > > > > +               return -ENODEV;
> > >
> > > At which circumstances may we get
> > >         dev != NULL
> > >         dev->dev == NULL
> > > ?
> > >
> > > ...
> > >
> > > > >         if (!dev || !dev->dev)
> > > > > -               return 0;
> > > > > +               return -ENODEV;
> > >
> > > I see the same here, perhaps Hans knows the answer :-)
> >
> > Right, so I must admit that I simply used *-baytrail.c as a reference and
> > thinking that additional check shouldn't hurt us (always better than not
> > enough safety..). Looking more at this now - `dw_i2c_plat_probe()` will
> > boil-out earlier if `dev->dev == NULL`. Should I remove this extra check in
> > *-baytrail.c in the same commit?
>
> Maybe. Please, double check that it's not needed indeed.

Confirmed that this is unnecessary.

Best Regards,
Jan

>
> --
> With Best Regards,
> Andy Shevchenko
>
>