linux-kernel - Re: [PATCH v3] scsi: ufs: Allow RTT negotiation

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Date: Tue, 14 May 2024 14:54:14 -0600
From: Bart Van Assche <bvanassche@....org>
To: Avri Altman <Avri.Altman@....com>,
 "Martin K . Petersen" <martin.petersen@...cle.com>
Cc: Bean Huo <beanhuo@...ron.com>, Peter Wang <peter.wang@...iatek.com>,
 "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] scsi: ufs: Allow RTT negotiation

On 5/14/24 14:34, Avri Altman wrote:
>> On 5/13/24 23:08, Avri Altman wrote:
>>> +/* bMaxNumOfRTT is equal to two after device manufacturing */
>>> +#define DEFAULT_MAX_NUM_RTT 2
>>> [ ... ]
>>> +     /* do not override if it was already written */
>>> +     if (dev_rtt != DEFAULT_MAX_NUM_RTT)
>>> +             return;
>>
>> I haven't found any text in the UFSHCI 4.0 specification that says
>> that the default value for the number of outstanding RTT requests
>> should be 2. Did I perhaps overlook something? If I didn't overlook
>> anything, the driver should not try to check whether dev_rtt is at its
>> default value.
> JEDEC Standard No. 220F Page 150 Line 2837 says: "bMaxNumOfRTT is equal to two after device manufacturing,"

Thanks Avri for having looked this up.

My understanding is that the above check won't work as intended if
ufshcd_rtt_set() does not modify the RTT value. Wouldn't it be better
to add a boolean in struct ufs_hba that indicates whether or not
ufshcd_rtt_set() has been called before?

Thanks,

Bart.