linux-kernel - Re: [EXT] [PATCH 2/3] scsi: ufs: Allow resetting the UFS device

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Date:   Tue, 4 Jun 2019 15:30:25 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     "Bean Huo (beanhuo)" <beanhuo@...ron.com>
Cc:     Pedro Sousa <pedrom.sousa@...opsys.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Andy Gross <agross@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>
Subject: Re: [EXT] [PATCH 2/3] scsi: ufs: Allow resetting the UFS device

On Tue 04 Jun 01:13 PDT 2019, Bean Huo (beanhuo) wrote:
> >@@ -6159,6 +6179,9 @@ static int ufshcd_reset_and_restore(struct ufs_hba
> >*hba)
> > 	int retries = MAX_HOST_RESET_RETRIES;
> >
> > 	do {
> >+		/* Reset the attached device */
> >+		ufshcd_device_reset(hba);
> >+
> 
> what's problem you met, and you should reset UFS device here? could you give more info?
> 
> It is true that we don't reset UFS device in case of device fatal error. According to UFS host spec,
> Host should be device reset except that in addition to resetting UIC. But as so far,
> We didn't experience any problems result from this missing reset.
> 
> We have three UFS device reset ways.  Comparing to this hardware reset, 
> I prefer to use DME_ENDPOINTRESET.req software reset.
> 

Hi Bean,

Thanks for your questions. With some memories we see issues establishing
the link during bootup, so that's the purpose of issuing this reset.

Unfortunately the downstream Qualcomm patch [1] (which I should have
remembered to attribute), does not mention why the reset during host
controller reset is needed - but I'm fairly certain that this scenario
would be similar to the handover from bootloader to kernel that we do
see an issue with.


[1] https://source.codeaurora.org/quic/la/kernel/msm-4.4/commit/?h=msm-4.4&id=0c82737188e2d63a08196e078e411032dbbc3b89

Regards,
Bjorn