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Subject: Re: [PATCH v6 1/6] scsi: ufs: Add "wb_on" sysfs node to control WB
 on/off
From:   Bean Huo <huobean@gmail.com>
To:     Adrian Hunter <adrian.hunter@intel.com>, alim.akhtar@samsung.com,
        avri.altman@wdc.com, asutoshd@codeaurora.org, 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:   Tue, 19 Jan 2021 10:33:45 +0100
In-Reply-To: <0a9971aa-e508-2aaa-1379-fb898471a252@intel.com>
References: <20210118201039.2398-1-huobean@gmail.com>
         <20210118201039.2398-2-huobean@gmail.com>
         <0a9971aa-e508-2aaa-1379-fb898471a252@intel.com>
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On Tue, 2021-01-19 at 09:01 +0200, Adrian Hunter wrote:
> On 18/01/21 10:10 pm, Bean Huo wrote:
> > From: Bean Huo <beanhuo@micron.com>
> > 
> > Currently UFS WriteBooster driver uses clock scaling up/down to set
> > WB on/off, for the platform which doesn't support
> > UFSHCD_CAP_CLK_SCALING,
> > WB will be always on. Provide a sysfs attribute to enable/disable
> > WB
> > during runtime. Write 1/0 to "wb_on" sysfs node to enable/disable
> > UFS WB.
> 
> Is it so, that after a full reset, WB is always enabled again?  Is
> that
> intended?

Hello Adrian
Good questions. yes, after a full reset, the UFS device side by default
is wb disabled,  then WB will be always enabled agaion in
ufshcd_wb_config(hba). but, for the platform which
supports UFSHCD_CAP_CLK_SCALING, wb will be disabled again while clk
scaling down and enabled while clk scaling up.

Regarding the last question, I think OEM wants to do that. maybe they
suppose there will be a lot of writing after reset?? From the UFS
device's point of view, the control of WB is up to the user.

Thanks,
Bean