linux-kernel - Re: [PATCH v2 5/6] scsi: ufs: Let host_sem cover the entire system suspend/resume

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Message-ID: <19b44731-1a4f-c88c-58fd-05eca5df2c2e@acm.org>
Date:   Mon, 24 May 2021 09:56:15 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Can Guo <cang@...eaurora.org>, asutoshd@...eaurora.org,
        nguyenb@...eaurora.org, hongwus@...eaurora.org,
        linux-scsi@...r.kernel.org, kernel-team@...roid.com
Cc:     Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Stanley Chu <stanley.chu@...iatek.com>,
        Bean Huo <beanhuo@...ron.com>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 5/6] scsi: ufs: Let host_sem cover the entire system
 suspend/resume

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.