linux-kernel - Re: [PATCH v1 1/2] scsi: ufs: Introduce a vops for resetting host controller

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Date:   Thu, 31 Oct 2019 07:44:29 -0700
From:   Mark Salyzyn <salyzyn@...roid.com>
To:     Can Guo <cang@...eaurora.org>, asutoshd@...eaurora.org,
        nguyenb@...eaurora.org, rnayak@...eaurora.org,
        linux-scsi@...r.kernel.org, kernel-team@...roid.com,
        saravanak@...gle.com, salyzyn@...gle.com
Cc:     Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>,
        Pedro Sousa <pedrom.sousa@...opsys.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Stanley Chu <stanley.chu@...iatek.com>,
        Bean Huo <beanhuo@...ron.com>,
        Tomas Winkler <tomas.winkler@...el.com>,
        Subhash Jadavani <subhashj@...eaurora.org>,
        Arnd Bergmann <arnd@...db.de>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 1/2] scsi: ufs: Introduce a vops for resetting host
 controller

On 10/22/19 9:13 PM, Can Guo wrote:
> Some UFS host controllers need their specific implementations of resetting
> to get them into a good state. Provide a new vops to allow the platform
> driver to implement this own reset operation.
>
> Signed-off-by: Can Guo <cang@...eaurora.org>
> ---
>   drivers/scsi/ufs/ufshcd.c | 16 ++++++++++++++++
>   drivers/scsi/ufs/ufshcd.h | 10 ++++++++++
>   2 files changed, 26 insertions(+)
>
> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> index c28c144..161e3c4 100644
> --- a/drivers/scsi/ufs/ufshcd.c
> +++ b/drivers/scsi/ufs/ufshcd.c
> @@ -3859,6 +3859,14 @@ static int ufshcd_link_recovery(struct ufs_hba *hba)
>   	ufshcd_set_eh_in_progress(hba);
>   	spin_unlock_irqrestore(hba->host->host_lock, flags);
>   
> +	ret = ufshcd_vops_full_reset(hba);
> +	if (ret)
> +		dev_warn(hba->dev, "%s: full reset returned %d\n",
> +				  __func__, ret);
> +
> +	/* Reset the attached device */
> +	ufshcd_vops_device_reset(hba);
> +
>   	ret = ufshcd_host_reset_and_restore(hba);
>   
>   	spin_lock_irqsave(hba->host->host_lock, flags);

In all your cases, especially after this adjustment, 
ufshcd_vops_full_reset is called blindly (+error checking message) 
before ufshcd_vops_device_reset. What about dropping the .full_reset 
(should really have been called .hw_reset or .host_reset) addition to 
the vops, just adding ufshcd_vops_device_reset call here before 
ufshcd_host_reset_and_restore, and in the driver folding the 
ufshcd_vops_full_reset code into the .device_reset handler?

Would that be workable? It would be simpler if so.

I can see a desire for the heads up 
(ufshcd_vops_full_reset+)ufshcd_vops_device_reset calls before 
ufshcd_host_reset_and_restore because that function will spin 10 seconds 
waiting for a response from a standardized register, that itself could 
be hardware locked up requiring product specific reset procedures. But 
if that is the case, then what about all the other calls to 
ufshcd_host_reset_and_restore in this file that are not provided the 
heads up? My guess is that the host device only demonstrated issues in 
the ufshcd_link_recovery handling path? Are you sure this is the only 
path that tickles the controller into a hardware lockup state?

Sincerely -- Mark Salyzyn