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

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Date: Tue, 14 May 2024 21:07:56 +0000
From: Avri Altman <Avri.Altman@....com>
To: Bart Van Assche <bvanassche@....org>, "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?
My intension was to not override RTT should it was written, e.g. from user space.
As this attribute is persistent.
See Bean's comment to v1.

Thanks,
Avri

> 
> Thanks,
> 
> Bart.