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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>
From:   "Asutosh Das (asd)" <asutoshd@codeaurora.org>
Message-ID: <2a380908-3eb4-2cdc-4156-03e8946ffd88@codeaurora.org>
Date:   Mon, 30 Nov 2020 15:19:05 -0800
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On 11/30/2020 10:11 AM, Bean Huo wrote:
> From: Bean Huo <beanhuo@micron.com>
> 
> Currently we let UFS WriteBooster driver use 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.
> 
> Signed-off-by: Bean Huo <beanhuo@micron.com>
> ---
>   drivers/scsi/ufs/ufs-sysfs.c | 33 +++++++++++++++++++++++++++++++++
>   drivers/scsi/ufs/ufshcd.c    |  3 +--
>   drivers/scsi/ufs/ufshcd.h    |  2 ++
>   3 files changed, 36 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/scsi/ufs/ufs-sysfs.c b/drivers/scsi/ufs/ufs-sysfs.c
> index 08e72b7eef6a..e41d8eb779ec 100644
> --- a/drivers/scsi/ufs/ufs-sysfs.c
> +++ b/drivers/scsi/ufs/ufs-sysfs.c
> @@ -189,6 +189,37 @@ static ssize_t auto_hibern8_store(struct device *dev,
>   	return count;
>   }
>   
> +static ssize_t wb_on_show(struct device *dev, struct device_attribute *attr,
> +			  char *buf)
> +{
> +	struct ufs_hba *hba = dev_get_drvdata(dev);
> +
> +	return scnprintf(buf, PAGE_SIZE, "%d\n", hba->wb_enabled);
> +}
> +
> +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_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);

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?

> +	pm_runtime_put_sync(hba->dev);
> +
> +	return res < 0 ? res : count;
> +}
> +
>   static DEVICE_ATTR_RW(rpm_lvl);
>   static DEVICE_ATTR_RO(rpm_target_dev_state);
>   static DEVICE_ATTR_RO(rpm_target_link_state);
> @@ -196,6 +227,7 @@ static DEVICE_ATTR_RW(spm_lvl);
>   static DEVICE_ATTR_RO(spm_target_dev_state);
>   static DEVICE_ATTR_RO(spm_target_link_state);
>   static DEVICE_ATTR_RW(auto_hibern8);
> +static DEVICE_ATTR_RW(wb_on);
>   
>   static struct attribute *ufs_sysfs_ufshcd_attrs[] = {
>   	&dev_attr_rpm_lvl.attr,
> @@ -205,6 +237,7 @@ static struct attribute *ufs_sysfs_ufshcd_attrs[] = {
>   	&dev_attr_spm_target_dev_state.attr,
>   	&dev_attr_spm_target_link_state.attr,
>   	&dev_attr_auto_hibern8.attr,
> +	&dev_attr_wb_on.attr,
>   	NULL
>   };
>   
> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> index d169db41ee16..639ba9d1ccbb 100644
> --- a/drivers/scsi/ufs/ufshcd.c
> +++ b/drivers/scsi/ufs/ufshcd.c
> @@ -247,7 +247,6 @@ static inline int ufshcd_config_vreg_hpm(struct ufs_hba *hba,
>   static int ufshcd_try_to_abort_task(struct ufs_hba *hba, int tag);
>   static int ufshcd_wb_buf_flush_enable(struct ufs_hba *hba);
>   static int ufshcd_wb_buf_flush_disable(struct ufs_hba *hba);
> -static int ufshcd_wb_ctrl(struct ufs_hba *hba, bool enable);
>   static int ufshcd_wb_toggle_flush_during_h8(struct ufs_hba *hba, bool set);
>   static inline void ufshcd_wb_toggle_flush(struct ufs_hba *hba, bool enable);
>   static void ufshcd_hba_vreg_set_lpm(struct ufs_hba *hba);
> @@ -5299,7 +5298,7 @@ static void ufshcd_bkops_exception_event_handler(struct ufs_hba *hba)
>   				__func__, err);
>   }
>   
> -static int ufshcd_wb_ctrl(struct ufs_hba *hba, bool enable)
> +int ufshcd_wb_ctrl(struct ufs_hba *hba, bool enable)
>   {
>   	int ret;
>   	u8 index;
> diff --git a/drivers/scsi/ufs/ufshcd.h b/drivers/scsi/ufs/ufshcd.h
> index d0b68df07eef..c7bb61a4e484 100644
> --- a/drivers/scsi/ufs/ufshcd.h
> +++ b/drivers/scsi/ufs/ufshcd.h
> @@ -1067,6 +1067,8 @@ int ufshcd_exec_raw_upiu_cmd(struct ufs_hba *hba,
>   			     u8 *desc_buff, int *buff_len,
>   			     enum query_opcode desc_op);
>   
> +int ufshcd_wb_ctrl(struct ufs_hba *hba, bool enable);
> +
>   /* Wrapper functions for safely calling variant operations */
>   static inline const char *ufshcd_get_var_name(struct ufs_hba *hba)
>   {
> 


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