linux-kernel - Re: [PATCH RFC v3 10/11] scsi: ufs: core: Perform read back to commit doorbell

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Date: Thu, 21 Dec 2023 11:28:42 -0800
From: Bart Van Assche <bvanassche@....org>
To: Andrew Halaney <ahalaney@...hat.com>, Andy Gross <agross@...nel.org>,
 Bjorn Andersson <andersson@...nel.org>,
 Konrad Dybcio <konrad.dybcio@...aro.org>,
 Manivannan Sadhasivam <mani@...nel.org>,
 "James E.J. Bottomley" <jejb@...ux.ibm.com>,
 "Martin K. Petersen" <martin.petersen@...cle.com>,
 Hannes Reinecke <hare@...e.de>, Janek Kotas <jank@...ence.com>,
 Alim Akhtar <alim.akhtar@...sung.com>, Avri Altman <avri.altman@....com>,
 Can Guo <quic_cang@...cinc.com>
Cc: Will Deacon <will@...nel.org>, linux-arm-msm@...r.kernel.org,
 linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC v3 10/11] scsi: ufs: core: Perform read back to commit
 doorbell

On 12/21/23 11:09, Andrew Halaney wrote:
> diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
> index 75a03ee9a1ba..caebd589e08c 100644
> --- a/drivers/ufs/core/ufshcd.c
> +++ b/drivers/ufs/core/ufshcd.c
> @@ -7050,7 +7050,7 @@ static int __ufshcd_issue_tm_cmd(struct ufs_hba *hba,
>   
>   	ufshcd_writel(hba, 1 << task_tag, REG_UTP_TASK_REQ_DOOR_BELL);
>   	/* Make sure that doorbell is committed immediately */
> -	wmb();
> +	ufshcd_readl(hba, REG_UTP_TASK_REQ_DOOR_BELL);
>   
>   	spin_unlock_irqrestore(host->host_lock, flags);

There is a wait_for_completion_io_timeout() call later in this function and
it is safe to write to the REG_UTP_TASK_REQ_DOOR_BELL register from multiple
threads concurrently so I think the above wmb() call can be left out entirely.

Thanks,

Bart.