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

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Message-id: <00a301d22038$5d4adb50$17e091f0$@samsung.com>
Date:   Fri, 07 Oct 2016 10:16:00 +0900
From:   Kiwoong Kim <kwmad.kim@...sung.com>
To:     'Subhash Jadavani' <subhashj@...eaurora.org>
Cc:     vinholikatti@...il.com, jejb@...ux.vnet.ibm.com,
        martin.petersen@...cle.com,
        "'open list:UNIVERSAL FLASH STORAGE HOST CONTROLLER DRIVER'" 
        <linux-scsi@...r.kernel.org>,
        'open list' <linux-kernel@...r.kernel.org>,
        linux-scsi-owner@...r.kernel.org
Subject: RE: [PATCH v2] scsi: ufshcd: fix possible unclocked register access

Hi, Subhash.

> Thanks Kim for the response.
> 
> On 2016-10-06 03:28, Kiwoong Kim wrote:
> > 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.
> 
> Are you suggesting to call ufshcd_vops_setup_clocks() 2 times, one before
> the on/off by ufshcd core driver and one after the on/off? If yes, then we
> also have add 3rd argument clarifying if this is PRE_CHANGE or
POST_CHANGE.
> 
> >
> > 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.
> 
> This is my suggestion:
> 1. Add 3rd argument to setup_clocks ops to let the vendor callback
> function know if this is called PRE_CHANGE or POST_CHANGE.
> 2. If #1 is in place, call setup_clocks 2 times, one with PRE_CHANGE
> argument before making any clock changes in core driver, 2nd with
> POST_CHANGE argument after making the clock changes to core driver.

Yes, that's exactly the same what I mean.

Thanks


> 
> Let me know if this would work or not.
> 
> Thanks,
> Subhash
> 
> >
> > 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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> >> in
> >> the body of a message to majordomo@...r.kernel.org
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> >
> >
> > --
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> > in
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> 
> --
> The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
> a Linux Foundation Collaborative Project
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