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

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