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Subject: Re: [PATCH v2 5/6] scsi: ufs: Let host_sem cover the entire system
 suspend/resume
To:     Can Guo <cang@codeaurora.org>, asutoshd@codeaurora.org,
        nguyenb@codeaurora.org, hongwus@codeaurora.org,
        linux-scsi@vger.kernel.org, kernel-team@android.com
Cc:     Alim Akhtar <alim.akhtar@samsung.com>,
        Avri Altman <avri.altman@wdc.com>,
        "James E.J. Bottomley" <jejb@linux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        Stanley Chu <stanley.chu@mediatek.com>,
        Bean Huo <beanhuo@micron.com>,
        Jaegeuk Kim <jaegeuk@kernel.org>,
        open list <linux-kernel@vger.kernel.org>
References: <1621846046-22204-1-git-send-email-cang@codeaurora.org>
 <1621846046-22204-6-git-send-email-cang@codeaurora.org>
From:   Bart Van Assche <bvanassche@acm.org>
Message-ID: <19b44731-1a4f-c88c-58fd-05eca5df2c2e@acm.org>
Date:   Mon, 24 May 2021 09:56:15 -0700
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On 5/24/21 1:47 AM, Can Guo wrote:
> UFS error handling now is doing more than just re-probing, but also sending
> scsi cmds, e.g., for clearing UACs, and recovering runtime PM error, which
> may change runtime status of scsi devices. To protect system suspend/resume
> from being disturbed by error handling, move the host_sem from wl pm ops
> to ufshcd_suspend_prepare() and ufshcd_resume_complete().

Other SCSI LLDs can perform error handling while system suspend/resume
is in progress. Why can't the UFS driver do this?

Additionally, please document what the purpose of host_sem is before
making any changes to how host_sem is used. The only documentation I
have found of host_sem is the following: "* @host_sem: semaphore used to
serialize concurrent contexts". To me that text is less than useful
since semaphores are almost always used to serialize concurrent code.

Thanks,

Bart.