linux-kernel - Re: [PATCH v3 01/25] bus: mhi: Fix pm

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Date:   Wed, 16 Feb 2022 07:41:56 -0600
From:   Alex Elder <elder@...aro.org>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     mhi@...ts.linux.dev, quic_hemantk@...cinc.com,
        quic_bbhatt@...cinc.com, quic_jhugo@...cinc.com,
        vinod.koul@...aro.org, bjorn.andersson@...aro.org,
        dmitry.baryshkov@...aro.org, quic_vbadigan@...cinc.com,
        quic_cang@...cinc.com, quic_skananth@...cinc.com,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Paul Davey <paul.davey@...iedtelesis.co.nz>,
        Hemant Kumar <hemantk@...eaurora.org>, stable@...r.kernel.org
Subject: Re: [PATCH v3 01/25] bus: mhi: Fix pm_state conversion to string

On 2/16/22 5:33 AM, Manivannan Sadhasivam wrote:
> On Tue, Feb 15, 2022 at 02:01:54PM -0600, Alex Elder wrote:
>> On 2/12/22 12:20 PM, Manivannan Sadhasivam wrote:
>>> From: Paul Davey <paul.davey@...iedtelesis.co.nz>
>>>
>>> On big endian architectures the mhi debugfs files which report pm state
>>> give "Invalid State" for all states.  This is caused by using
>>> find_last_bit which takes an unsigned long* while the state is passed in
>>> as an enum mhi_pm_state which will be of int size.
>>
>> I think this would have fixed it too, but your fix is better.
>>
>> 	int index = find_last_bit(&(unsigned long)state, 32);
>>
>>> Fix by using __fls to pass the value of state instead of find_last_bit.
>>>
>>> Fixes: a6e2e3522f29 ("bus: mhi: core: Add support for PM state transitions")
>>> Signed-off-by: Paul Davey <paul.davey@...iedtelesis.co.nz>
>>> Reviewed-by: Manivannan Sadhasivam <mani@...nel.org>
>>> Reviewed-by: Hemant Kumar <hemantk@...eaurora.org>
>>> Cc: stable@...r.kernel.org
>>> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
>>> ---
>>>    drivers/bus/mhi/core/init.c | 8 +++++---
>>>    1 file changed, 5 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/bus/mhi/core/init.c b/drivers/bus/mhi/core/init.c
>>> index 046f407dc5d6..af484b03558a 100644
>>> --- a/drivers/bus/mhi/core/init.c
>>> +++ b/drivers/bus/mhi/core/init.c
>>> @@ -79,10 +79,12 @@ static const char * const mhi_pm_state_str[] = {
>>>    const char *to_mhi_pm_state_str(enum mhi_pm_state state)
>>
>> The mhi_pm_state enumerated type is an enumerated sequence, not
>> a bit mask.  So knowing what the last (most significant) set bit
>> is not meaningful.  Or normally it shouldn't be.
>>
>> If mhi_pm_state really were a bit mask, then its values should
>> be defined that way, i.e.,
>>
>> 	MHI_PM_STATE_DISABLE	= 1 << 0,
>> 	MHI_PM_STATE_DISABLE	= 1 << 1,
>> 	. . .
>>
>> What's really going on is that the state value passed here
>> *is* a bitmask, whose bit positions are those mhi_pm_state
>> values.  So the state argument should have type u32.
>>
> 
> I agree with you. It should be u32.
> 
>> This is a *separate* bug/issue.  It could be fixed separately
>> (before this patch), but I'd be OK with just explaining why
>> this change would occur as part of this modified patch.
>>
> 
> It makes sense to do it in the same patch itself as the change is
> minimal and moreover this patch will also get backported to stable.

Sounds good to me.	-Alex

>>>    {
>>> -	unsigned long pm_state = state;
>>> -	int index = find_last_bit(&pm_state, 32);
>>> +	int index;
>>> -	if (index >= ARRAY_SIZE(mhi_pm_state_str))
>>> +	if (state)
>>> +		index = __fls(state);
>>> +
>>> +	if (!state || index >= ARRAY_SIZE(mhi_pm_state_str))
>>>    		return "Invalid State";
>>
>> Do this test and return first, and skip the additional
>> check for "if (state)".
>>
> 
> We need to calculate index for the second check, so I guess the current
> code is fine.
> 
> Thanks,
> Mani
> 
>> 					-Alex
>>
>>>    	return mhi_pm_state_str[index];
>>