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Subject: Re: [PATCH 1/3] scsi: ufs: Add "wb_on" sysfs node to control WB
 on/off
To:     Bean Huo <huobean@gmail.com>, 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
References: <20201130181143.5739-1-huobean@gmail.com>
 <20201130181143.5739-2-huobean@gmail.com>
 <2a380908-3eb4-2cdc-4156-03e8946ffd88@codeaurora.org>
 <30767ee7973670b86bff61d1d7b2044f17640b75.camel@gmail.com>
From:   "Asutosh Das (asd)" <asutoshd@codeaurora.org>
Message-ID: <64458f93-55ed-ae62-e7c2-d4c54721b2b1@codeaurora.org>
Date:   Wed, 2 Dec 2020 09:58:29 -0800
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On 12/2/2020 8:20 AM, Bean Huo wrote:
> 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:

Or a synchronization primitive b/w the 2 contexts would work just as 
well. However, I don't have an issue if the user is denied toggling of 
wb anyway. LGTM.

> 
> 
> +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
> 
> 


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