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Subject: Re: [PATCH 1/3] scsi: ufs: Add "wb_on" sysfs node to control WB
 on/off
From:   Bean Huo <huobean@gmail.com>
To:     "Asutosh Das (asd)" <asutoshd@codeaurora.org>,
        alim.akhtar@samsung.com, avri.altman@wdc.com, jejb@linux.ibm.com,
        martin.petersen@oracle.com, stanley.chu@mediatek.com,
        beanhuo@micron.com, bvanassche@acm.org, tomas.winkler@intel.com,
        cang@codeaurora.org
Cc:     linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org
Date:   Wed, 02 Dec 2020 17:20:45 +0100
In-Reply-To: <2a380908-3eb4-2cdc-4156-03e8946ffd88@codeaurora.org>
References: <20201130181143.5739-1-huobean@gmail.com>
         <20201130181143.5739-2-huobean@gmail.com>
         <2a380908-3eb4-2cdc-4156-03e8946ffd88@codeaurora.org>
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On Mon, 2020-11-30 at 15:19 -0800, Asutosh Das (asd) wrote:
> > +             return -EINVAL;
> > +
> > +     pm_runtime_get_sync(hba->dev);
> > +     res = ufshcd_wb_ctrl(hba, wb_enable);
> 
> Say, a platform supports clock-scaling and this bit is toggled.
> The control goes into ufshcd_wb_ctrl for both this sysfs and 
> clock-scaling contexts. The clock-scaling context passes all checks
> and 
> blocks on waiting for this wb control to be disabled and then tries
> to 
> enable wb when it's already disabled. Perhaps that's a race there?

Hi Asutosh
Appreciate your review.
There is only inconsistent problem between clock-scaling and sysfs,
since hba->dev_cmd.lock can garantee there is only one can change
fWriteBoosterEn. But this is only happening on user willfully wants to
control WB through sysfs even they know the platform supports clock-
scaling.

Since this is for the platform which doesn't support clock-scaling, I
think based on your comments, it should be acceptable for you like
this: 


+static ssize_t wb_on_store(struct device *dev, struct device_attribute
*attr,
+                          const char *buf, size_t count)
+{
+       struct ufs_hba *hba = dev_get_drvdata(dev);
+       unsigned int wb_enable;
+       ssize_t res;
+
+       if (ufshcd_is_clkscaling_supported(hba)) {
+          dev_err(dev, "supports dynamic clk scaling, control WB
+                       through sysfs is not allowed!");
+          return -EOPNOTSUPP;
+       } 
+       if (!ufshcd_is_wb_allowed(hba))
+               return -EOPNOTSUPP;
+
+       if (kstrtouint(buf, 0, &wb_enable))
+               return -EINVAL;
+
+       if (wb_enable != 0 && wb_enable != 1)
+               return -EINVAL;
+
+       pm_runtime_get_sync(hba->dev);
+       res = ufshcd_wb_ctrl(hba, wb_enable);
+       pm_runtime_put_sync(hba->dev);
+
+       return res < 0 ? res : count;
+}

thanks,
Bean