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

From: Mark Salyzyn <salyzyn@android.com>
To: Can Guo <cang@codeaurora.org>,
	asutoshd@codeaurora.org, nguyenb@codeaurora.org,
	rnayak@codeaurora.org, linux-scsi@vger.kernel.org,
	kernel-team@android.com, saravanak@google.com,
	salyzyn@google.com
Cc: Alim Akhtar <alim.akhtar@samsung.com>,
	Avri Altman <avri.altman@wdc.com>,
	Pedro Sousa <pedrom.sousa@synopsys.com>,
	"James E.J. Bottomley" <jejb@linux.ibm.com>,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	Stanley Chu <stanley.chu@mediatek.com>,
	Bean Huo <beanhuo@micron.com>,
	Tomas Winkler <tomas.winkler@intel.com>,
	Subhash Jadavani <subhashj@codeaurora.org>,
	Arnd Bergmann <arnd@arndb.de>,
	Bjorn Andersson <bjorn.andersson@linaro.org>,
	open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v1 1/2] scsi: ufs: Introduce a vops for resetting host controller
Date: Thu, 31 Oct 2019 07:44:29 -0700	[thread overview]
Message-ID: <61b83149-e89b-bb4c-d747-a4c596c8eede@android.com> (raw)
In-Reply-To: <1571804009-29787-2-git-send-email-cang@codeaurora.org>

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@codeaurora.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