Re: [PATCH RFC] ufs: Make ufshcd_wait_for_register() sleep instead of busy-waiting

["Asutosh Das (asd)" <asutoshd@codeaurora.org>]

On 5/7/2020 3:27 PM, Bart Van Assche wrote:
> The ufshcd_wait_for_register() function either sleeps or spins until the
> specified register has reached the desired value. Busy-waiting is not
> only considered a bad practice but also has a bad impact on energy
> consumption. Always sleep instead of spinning by making sure that all
> ufshcd_wait_for_register() calls happen from a context where it is
> allowed to sleep. The only function call that has to be moved is the
> ufshcd_hba_stop() call in ufshcd_host_reset_and_restore().
> 
> Cc: Can Guo <cang@codeaurora.org>
> Cc: Avri Altman <avri.altman@wdc.com>
> Cc: Bean Huo <beanhuo@micron.com>
> Cc: Alim Akhtar <alim.akhtar@samsung.com>
> Cc: Asutosh Das <asutoshd@codeaurora.org>
> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
> ---
Reviewed-by: Asutosh Das <asutoshd@codeaurora.org>


>   drivers/scsi/ufs/ufshcd.c | 51 +++++++++++++++++++++------------------
>   drivers/scsi/ufs/ufshcd.h |  2 +-
>   2 files changed, 29 insertions(+), 24 deletions(-)
> 
> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> index bf7caea2253b..72069d4faa1e 100644
> --- a/drivers/scsi/ufs/ufshcd.c
> +++ b/drivers/scsi/ufs/ufshcd.c
> @@ -563,21 +563,21 @@ void ufshcd_delay_us(unsigned long us, unsigned long tolerance)
>   }
>   EXPORT_SYMBOL_GPL(ufshcd_delay_us);
>   
> -/*
> +/**
>    * ufshcd_wait_for_register - wait for register value to change
> - * @hba - per-adapter interface
> - * @reg - mmio register offset
> - * @mask - mask to apply to read register value
> - * @val - wait condition
> - * @interval_us - polling interval in microsecs
> - * @timeout_ms - timeout in millisecs
> - * @can_sleep - perform sleep or just spin
> + * @hba: per-adapter interface
> + * @reg: mmio register offset
> + * @mask: mask to apply to the read register value
> + * @val: value to wait for
> + * @interval_us: polling interval in microseconds
> + * @timeout_ms: timeout in milliseconds
>    *
> - * Returns -ETIMEDOUT on error, zero on success
> + * Return:
> + * -ETIMEDOUT on error, zero on success.
>    */
>   int ufshcd_wait_for_register(struct ufs_hba *hba, u32 reg, u32 mask,
>   				u32 val, unsigned long interval_us,
> -				unsigned long timeout_ms, bool can_sleep)
> +				unsigned long timeout_ms)
>   {
>   	int err = 0;
>   	unsigned long timeout = jiffies + msecs_to_jiffies(timeout_ms);
> @@ -586,10 +586,7 @@ int ufshcd_wait_for_register(struct ufs_hba *hba, u32 reg, u32 mask,
>   	val = val & mask;
>   
>   	while ((ufshcd_readl(hba, reg) & mask) != val) {
> -		if (can_sleep)
> -			usleep_range(interval_us, interval_us + 50);
> -		else
> -			udelay(interval_us);
> +		usleep_range(interval_us, interval_us + 50);
>   		if (time_after(jiffies, timeout)) {
>   			if ((ufshcd_readl(hba, reg) & mask) != val)
>   				err = -ETIMEDOUT;
> @@ -2589,7 +2586,7 @@ ufshcd_clear_cmd(struct ufs_hba *hba, int tag)
>   	 */
>   	err = ufshcd_wait_for_register(hba,
>   			REG_UTP_TRANSFER_REQ_DOOR_BELL,
> -			mask, ~mask, 1000, 1000, true);
> +			mask, ~mask, 1000, 1000);
>   
>   	return err;
>   }
> @@ -4258,16 +4255,23 @@ EXPORT_SYMBOL_GPL(ufshcd_make_hba_operational);
>   /**
>    * ufshcd_hba_stop - Send controller to reset state
>    * @hba: per adapter instance
> - * @can_sleep: perform sleep or just spin
>    */
> -static inline void ufshcd_hba_stop(struct ufs_hba *hba, bool can_sleep)
> +static inline void ufshcd_hba_stop(struct ufs_hba *hba)
>   {
> +	unsigned long flags;
>   	int err;
>   
> +	/*
> +	 * Obtain the host lock to prevent that the controller is disabled
> +	 * while the UFS interrupt handler is active on another CPU.
> +	 */
> +	spin_lock_irqsave(hba->host->host_lock, flags);
>   	ufshcd_writel(hba, CONTROLLER_DISABLE,  REG_CONTROLLER_ENABLE);
> +	spin_unlock_irqrestore(hba->host->host_lock, flags);
> +
>   	err = ufshcd_wait_for_register(hba, REG_CONTROLLER_ENABLE,
>   					CONTROLLER_ENABLE, CONTROLLER_DISABLE,
> -					10, 1, can_sleep);
> +					10, 1);
>   	if (err)
>   		dev_err(hba->dev, "%s: Controller disable failed\n", __func__);
>   }
> @@ -4288,7 +4292,7 @@ int ufshcd_hba_enable(struct ufs_hba *hba)
>   
>   	if (!ufshcd_is_hba_active(hba))
>   		/* change controller state to "reset state" */
> -		ufshcd_hba_stop(hba, true);
> +		ufshcd_hba_stop(hba);
>   
>   	/* UniPro link is disabled at this point */
>   	ufshcd_set_link_off(hba);
> @@ -5911,7 +5915,7 @@ static int ufshcd_clear_tm_cmd(struct ufs_hba *hba, int tag)
>   	/* poll for max. 1 sec to clear door bell register by h/w */
>   	err = ufshcd_wait_for_register(hba,
>   			REG_UTP_TASK_REQ_DOOR_BELL,
> -			mask, 0, 1000, 1000, true);
> +			mask, 0, 1000, 1000);
>   out:
>   	return err;
>   }
> @@ -6478,8 +6482,9 @@ static int ufshcd_host_reset_and_restore(struct ufs_hba *hba)
>   	 * Stop the host controller and complete the requests
>   	 * cleared by h/w
>   	 */
> +	ufshcd_hba_stop(hba);
> +
>   	spin_lock_irqsave(hba->host->host_lock, flags);
> -	ufshcd_hba_stop(hba, false);
>   	hba->silence_err_logs = true;
>   	ufshcd_complete_requests(hba);
>   	hba->silence_err_logs = false;
> @@ -7986,7 +7991,7 @@ static int ufshcd_link_state_transition(struct ufs_hba *hba,
>   		 * Change controller state to "reset state" which
>   		 * should also put the link in off/reset state
>   		 */
> -		ufshcd_hba_stop(hba, true);
> +		ufshcd_hba_stop(hba);
>   		/*
>   		 * TODO: Check if we need any delay to make sure that
>   		 * controller is reset
> @@ -8545,7 +8550,7 @@ void ufshcd_remove(struct ufs_hba *hba)
>   	scsi_remove_host(hba->host);
>   	/* disable interrupts */
>   	ufshcd_disable_intr(hba, hba->intr_mask);
> -	ufshcd_hba_stop(hba, true);
> +	ufshcd_hba_stop(hba);
>   
>   	ufshcd_exit_clk_scaling(hba);
>   	ufshcd_exit_clk_gating(hba);
> diff --git a/drivers/scsi/ufs/ufshcd.h b/drivers/scsi/ufs/ufshcd.h
> index 733722840794..5c944530cde5 100644
> --- a/drivers/scsi/ufs/ufshcd.h
> +++ b/drivers/scsi/ufs/ufshcd.h
> @@ -822,7 +822,7 @@ int ufshcd_uic_hibern8_exit(struct ufs_hba *hba);
>   void ufshcd_delay_us(unsigned long us, unsigned long tolerance);
>   int ufshcd_wait_for_register(struct ufs_hba *hba, u32 reg, u32 mask,
>   				u32 val, unsigned long interval_us,
> -				unsigned long timeout_ms, bool can_sleep);
> +				unsigned long timeout_ms);
>   void ufshcd_parse_dev_ref_clk_freq(struct ufs_hba *hba, struct clk *refclk);
>   void ufshcd_update_reg_hist(struct ufs_err_reg_hist *reg_hist,
>   			    u32 reg);
> 


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