Re: [PATCH v2 1/1] i3c: Add fallback method for GETMXDS CCC

Miquel Raynal
2023-11-14T08:56:48Z

Hi Joshua,

joshua.yeong@starfivetech.com wrote on Tue, 14 Nov 2023 16:42:44 +0800:

> Hi Miquel,
>
> On 14-Nov-23 4:19 PM, Miquel Raynal wrote:
> > Hi Joshua,
> >
> > joshua.yeong@starfivetech.com wrote on Tue, 14 Nov 2023 11:34:30 +0800:
> >
> >> Some I3C hardware will report error when incorrect length is received from
> > an
> >
> >> device. GETMXDS CCC are availble in 2 formats; without turnaround time
> (format
> > available :
> >
> >> 1) and with turnaround time (format 2). There is no mechanics to deter
> mine which
> >> format is supported by device. In case sending GETMXDS CCC format 2 re
> sulted
> > So in case?
> >
> >> failure, try sending GETMXDS CCC format 1 instead.
> > in a
> >
> >> Signed-off-by: Joshua Yeong <joshua.yeong@starfivetech.com>
> >> ---
> >> drivers/i3c/master.c | 12 ++++++++++--
> >> 1 file changed, 10 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/i3c/master.c b/drivers/i3c/master.c
> >> index 0cdc94e4cb77..2fc04d97f07e 100644
> >> --- a/drivers/i3c/master.c
> >> +++ b/drivers/i3c/master.c
> >> @@ -1099,8 +1099,16 @@ static int i3c_master_getmxds_locked(struct i3c
> _master_controller *master,
> >> >> i3c_ccc_cmd_init(&cmd, true, I3C_CCC_GETMXDS, &dest, 1);
> >> ret = i3c_master_send_ccc_cmd_locked(master, &cmd);
> >> - if (ret)
> >> - goto out;
> >> + if (ret) {
> >> + /*
> > ^
> > Wrong alignment of the starts below
> > v
> >> + * Retry when the device does not support max read turnaround
> >> + * while expecting shorter length from this CCC command
> > period?
> >
> >> + */
> >> + dest->payload.len -= 3;
> >> + ret = i3c_master_send_ccc_cmd_locked(master, &cmd);
> >> + if (ret)
> >> + goto out;
> >> + }
> > I believe this is a per-device configuration and we should save this in
> > order to only fail once, no?
>
> This behavior depends on the hardware designed whether it will return an error
> in case of shorter length from i3c devices in dest->payload.len. I made it so it
> will retry by expecting a shorter length instead, in case it still fails then
> it means GETMXDS CCC really failed.

Yes, I got the logic.

> We do not have to initialize the same hardware twice and do GETMXDS CCC m
> ore
> than once as far as I know?

I don't remember. If you say so, then it's fine like this.

> >> >> if (dest.payload.len != 2 && dest.payload.len != 5) {
> >> ret = -EIO;

Thanks,
Miquèl