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

Alex Elder
2022-02-15T20:02:02Z

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.

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.

> {
> - 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)".

-Alex

> return mhi_pm_state_str[index];