Re: [PATCH v3 01/25] bus: mhi: Fix pm_state conversion to string

Alex Elder
2022-02-16T13:42:02Z

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@alliedtelesis.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@alliedtelesis.co.nz>
>>> Reviewed-by: Manivannan Sadhasivam <mani@kernel.org>
>>> Reviewed-by: Hemant Kumar <hemantk@codeaurora.org>
>>> Cc: stable@vger.kernel.org
>>> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.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];
>>