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

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Message-ID: <e00fa237216d667cff08e4268bb0d2f7@codeaurora.org>
Date:   Thu, 06 Oct 2016 12:03:56 -0700
From:   Subhash Jadavani <subhashj@...eaurora.org>
To:     Kiwoong Kim <kwmad.kim@...sung.com>
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

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.

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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> 
> 
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-- 
The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project