linux-kernel - Re: [PATCH v3 5/9] scsi: ufs: Simplify error handling preparation

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Date:   Fri, 11 Jun 2021 13:58:09 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Can Guo <cang@...eaurora.org>,
        Adrian Hunter <adrian.hunter@...el.com>
Cc:     asutoshd@...eaurora.org, nguyenb@...eaurora.org,
        hongwus@...eaurora.org, ziqichen@...eaurora.org,
        linux-scsi@...r.kernel.org, kernel-team@...roid.com,
        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 v3 5/9] scsi: ufs: Simplify error handling preparation

On 6/10/21 8:01 PM, Can Guo wrote:
> Previously, without commit cb7e6f05fce67c965194ac04467e1ba7bc70b069, 
> ufshcd_resume() may turn off pwr and clk due to UFS error, e.g., link
> transition failure and SSU error/abort (and these UFS error would
> invoke error handling).  When error handling kicks start, it should
> re-enable the pwr and clk before proceeding. Now, commit 
> cb7e6f05fce67c965194ac04467e1ba7bc70b069 makes ufshcd_resume()
> purely control pwr and clk, meaning if ufshcd_resume() fails, there
> is nothing we can do about it - pwr or clk enabling must have failed,
> and it is not because of UFS error. This is why I am removing the
> re-enabling pwr/clk in error handling prepare.

Why are link transition failures handled in the error handler instead of
in the context where these errors are detected (ufshcd_resume())? Is it
even possible to recover from a link transition failure or does this
perhaps indicate a broken UFS controller?

>> but what I really wonder is why we don't just do recovery directly
>> in __ufshcd_wl_suspend() and  __ufshcd_wl_resume() and strip all 
>> the PM complexity out of ufshcd_err_handling()?

+1

> For system suspend/resume, since error handling has the same nature
> like user access, so we are using host_sem to avoid concurrency of
> error handling and system suspend/resume.

Why is host_sem used for that purpose instead of lock_system_sleep() and
unlock_system_sleep()?

Thanks,

Bart.