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Subject: Re: [PATCH v2 3/4] ufs: ufs-qcom: Fix a few BUGs in func
 ufs_qcom_dump_dbg_regs()
To:     Can Guo <cang@codeaurora.org>, asutoshd@codeaurora.org,
        nguyenb@codeaurora.org, hongwus@codeaurora.org,
        rnayak@codeaurora.org, linux-scsi@vger.kernel.org,
        kernel-team@android.com, saravanak@google.com, salyzyn@google.com
Cc:     Andy Gross <agross@kernel.org>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Alim Akhtar <alim.akhtar@samsung.com>,
        Avri Altman <avri.altman@wdc.com>,
        "James E.J. Bottomley" <jejb@linux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        "open list:ARM/QUALCOMM SUPPORT" <linux-arm-msm@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>
References: <1594693693-22466-1-git-send-email-cang@codeaurora.org>
 <1594693693-22466-4-git-send-email-cang@codeaurora.org>
From:   Bart Van Assche <bvanassche@acm.org>
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Date:   Mon, 13 Jul 2020 20:47:18 -0700
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On 2020-07-13 19:28, Can Guo wrote:
> Dumping testbus registers needs to sleep a bit intermittently as there are
> too many of them. Skip them for those contexts where sleep is not allowed.
> 
> Meanwhile, if ufs_qcom_dump_dbg_regs() calls ufs_qcom_testbus_config() from
> ufshcd_suspend/resume and/or clk gate/ungate context, pm_runtime_get_sync()
> and ufshcd_hold() will cause racing problems. Fix it by removing the
> unnecessary calls of pm_runtime_get_sync() and ufshcd_hold().
> 
> Signed-off-by: Can Guo <cang@codeaurora.org>
> ---
>  drivers/scsi/ufs/ufs-qcom.c | 17 +++++++----------
>  1 file changed, 7 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/scsi/ufs/ufs-qcom.c b/drivers/scsi/ufs/ufs-qcom.c
> index 2e6ddb5..3743c17 100644
> --- a/drivers/scsi/ufs/ufs-qcom.c
> +++ b/drivers/scsi/ufs/ufs-qcom.c
> @@ -1604,9 +1604,6 @@ int ufs_qcom_testbus_config(struct ufs_qcom_host *host)
>  	 */
>  	}
>  	mask <<= offset;
> -
> -	pm_runtime_get_sync(host->hba->dev);
> -	ufshcd_hold(host->hba, false);
>  	ufshcd_rmwl(host->hba, TEST_BUS_SEL,
>  		    (u32)host->testbus.select_major << 19,
>  		    REG_UFS_CFG1);
> @@ -1619,8 +1616,6 @@ int ufs_qcom_testbus_config(struct ufs_qcom_host *host)
>  	 * committed before returning.
>  	 */
>  	mb();
> -	ufshcd_release(host->hba);
> -	pm_runtime_put_sync(host->hba->dev);
>  
>  	return 0;
>  }
> @@ -1658,11 +1653,13 @@ static void ufs_qcom_dump_dbg_regs(struct ufs_hba *hba)
>  
>  	/* sleep a bit intermittently as we are dumping too much data */
>  	ufs_qcom_print_hw_debug_reg_all(hba, NULL, ufs_qcom_dump_regs_wrapper);
> -	udelay(1000);
> -	ufs_qcom_testbus_read(hba);
> -	udelay(1000);
> -	ufs_qcom_print_unipro_testbus(hba);
> -	udelay(1000);
> +	if (in_task()) {
> +		udelay(1000);
> +		ufs_qcom_testbus_read(hba);
> +		udelay(1000);
> +		ufs_qcom_print_unipro_testbus(hba);
> +		udelay(1000);
> +	}
>  }

It is not clear to me how udelay() calls can help in code that takes long
since these functions use busy-waiting? Should the udelay() calls perhaps
be changed into cond_resched() calls?

Thanks,

Bart.