linux-kernel - Re: [PATCH v4 3/8] ufs: ufs-qcom: Fix a few BUGs in func ufs_qcom_dump_dbg

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Date:   Wed, 22 Jul 2020 08:37:19 -0600
From:   Jeffrey Hugo <jeffrey.l.hugo@...il.com>
To:     Can Guo <cang@...eaurora.org>
Cc:     Asutosh Das <asutoshd@...eaurora.org>, nguyenb@...eaurora.org,
        hongwus@...eaurora.org, Rajendra Nayak <rnayak@...eaurora.org>,
        sh425.lee@...sung.com, linux-scsi@...r.kernel.org,
        kernel-team@...roid.com, saravanak@...gle.com,
        Mark Salyzyn <salyzyn@...gle.com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        "open list:ARM/QUALCOMM SUPPORT" <linux-arm-msm@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 3/8] ufs: ufs-qcom: Fix a few BUGs in func ufs_qcom_dump_dbg_regs()

On Mon, Jul 20, 2020 at 12:39 AM Can Guo <cang@...eaurora.org> 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().

It sounds like this is two different changes which are clubbed
together into the same patch and really should be two different
patches.

>
> Signed-off-by: Can Guo <cang@...eaurora.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);
> +       }

Did you run into a specific issue with this?  udelay is not a "sleep"
in the sense that it causes scheduling to occur, which is the problem
with atomic contexts.