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

[Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>]

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.

> >   {
> > -	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];
>