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

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Message-ID: <d0e473f3-7b05-2d18-9874-eb9fe26f8478@starfivetech.com>
Date:   Tue, 14 Nov 2023 16:42:44 +0800
From:   Joshua Yeong <joshua.yeong@...rfivetech.com>
To:     Miquel Raynal <miquel.raynal@...tlin.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 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 determine which
>> format is supported by device. In case sending GETMXDS CCC format 2 resulted
> 				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.

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

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