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Date: Tue, 20 Feb 2024 10:19:45 -0800
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Subject: Re: [PATCH] scsi: ufs: core: Fix setup_xfer_req invocation
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To: Rohit Ner <rohitner@google.com>
Cc: Can Guo <quic_cang@quicinc.com>, Bean Huo <beanhuo@micron.com>,
 Stanley Chu <stanley.chu@mediatek.com>,
 "Martin K. Petersen" <martin.petersen@oracle.com>,
 Jaegeuk Kim <jaegeuk@kernel.org>, Avri Altman <avri.altman@wdc.com>,
 linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20240220090805.2886914-1-rohitner@google.com>
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 <CAGt9f=Qd8P4OUuT=KJQqpwJPYVB7zeCJjWn_4CTiXWce6ZRERg@mail.gmail.com>
From: Bart Van Assche <bvanassche@acm.org>
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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.