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

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Message-ID: <20231114095641.1068437e@xps-13>
Date:   Tue, 14 Nov 2023 09:56:41 +0100
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Joshua Yeong <joshua.yeong@...rfivetech.com>
Cc:     <alexandre.belloni@...tlin.com>, <linux-i3c@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/1] i3c: Add fallback method for GETMXDS CCC

Hi Joshua,

joshua.yeong@...rfivetech.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@...rfivetech.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@...rfivetech.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