linux-kernel - RE: [PATCH v2] scsi: ufshcd: fix possible unclocked register access

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Message-id: <000401d21fbc$62fd3600$28f7a200$@samsung.com>
Date:   Thu, 06 Oct 2016 19:28:32 +0900
From:   Kiwoong Kim <kwmad.kim@...sung.com>
To:     'Subhash Jadavani' <subhashj@...eaurora.org>,
        vinholikatti@...il.com, jejb@...ux.vnet.ibm.com,
        martin.petersen@...cle.com
Cc:     "'open list:UNIVERSAL FLASH STORAGE HOST CONTROLLER DRIVER'" 
        <linux-scsi@...r.kernel.org>,
        'open list' <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2] scsi: ufshcd: fix possible unclocked register access

Hi, Subhash.

Some UFS host controllers may need to call the vendor specific callback
before and after controlling by clock control framework,
regardless of whether available clocks are turned on or off.

Is there any special reason to limit to invoke the callback
only when the clocks are turned on or not?
Besides, the callback is acknowledged from core driver
because 2nd argument is whether the clocks are turned on or not.

If you have any other idea, please let me know.

Thanks
Regards

> Vendor specific setup_clocks callback may require the clocks managed
> by ufshcd driver to be ON. So if the vendor specific setup_clocks callback
> is called while the required clocks are turned off, it could result into
> unclocked register access.
> 
> To prevent possible unclock register access, this change makes sure that
> required clocks remain enabled before calling into vendor specific
> setup_clocks callback.
> 
> Signed-off-by: Subhash Jadavani <subhashj@...eaurora.org>
> ---
> Changes from v2:
> * Don't call ufshcd_vops_setup_clocks() again for clock off
> ---
>  drivers/scsi/ufs/ufshcd.c | 22 +++++++++++++++++++++-
>  1 file changed, 21 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> index 05c7456..c1a77d3 100644
> --- a/drivers/scsi/ufs/ufshcd.c
> +++ b/drivers/scsi/ufs/ufshcd.c
> @@ -5389,6 +5389,17 @@ static int __ufshcd_setup_clocks(struct ufs_hba
> *hba, bool on,
>  	if (!head || list_empty(head))
>  		goto out;
> 
> +	/*
> +	 * vendor specific setup_clocks ops may depend on clocks managed by
> +	 * this standard driver hence call the vendor specific setup_clocks
> +	 * before disabling the clocks managed here.
> +	 */
> +	if (!on) {
> +		ret = ufshcd_vops_setup_clocks(hba, on);
> +		if (ret)
> +			return ret;
> +	}
> +
>  	list_for_each_entry(clki, head, list) {
>  		if (!IS_ERR_OR_NULL(clki->clk)) {
>  			if (skip_ref_clk && !strcmp(clki->name, "ref_clk"))
> @@ -5410,7 +5421,16 @@ static int __ufshcd_setup_clocks(struct ufs_hba
> *hba, bool on,
>  		}
>  	}
> 
> -	ret = ufshcd_vops_setup_clocks(hba, on);
> +	/*
> +	 * vendor specific setup_clocks ops may depend on clocks managed by
> +	 * this standard driver hence call the vendor specific setup_clocks
> +	 * after enabling the clocks managed here.
> +	 */
> +	if (on) {
> +		ret = ufshcd_vops_setup_clocks(hba, on);
> +		if (ret)
> +			return ret;
> +	}
>  out:
>  	if (ret) {
>  		list_for_each_entry(clki, head, list) {
> --
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project
> 
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