linux-kernel - Re: [PATCH] scsi: ufs: core: Fix setup_xfer

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Message-ID: <f55c36c5-0b8f-4b7a-a0b9-b11320781a4f@acm.org>
Date: Tue, 20 Feb 2024 10:19:45 -0800
From: Bart Van Assche <bvanassche@....org>
To: Rohit Ner <rohitner@...gle.com>
Cc: Can Guo <quic_cang@...cinc.com>, Bean Huo <beanhuo@...ron.com>,
 Stanley Chu <stanley.chu@...iatek.com>,
 "Martin K. Petersen" <martin.petersen@...cle.com>,
 Jaegeuk Kim <jaegeuk@...nel.org>, Avri Altman <avri.altman@....com>,
 linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] scsi: ufs: core: Fix setup_xfer_req invocation

On 2/20/24 09:58, Rohit Ner wrote:
> Do you propose to remove this callback altogether? This callback should
> either support both transfer modes or none.

The only UFSHCI controller I know of that needs this callback is the Exynos
UFSHCI controller. As far as I know there are Exynos UFSHCI controllers that
support UFSHCI 3.0 but UFSHCI 4.0 Exynos controllers are not yet available.
Standard compliant controllers should not use the .setup_xfer_req() callback.
As you may know invoking that callback means performing an indirect function
call. Indirect function calls are slower than direct calls, especially if
speculative execution  vulnerability security mitigations are enabled.

Bart.