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    SubjectRe: [PATCH v4 8/8] bus: mhi: core: Ensure non-zero session or sequence ID values are used
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    On 5/1/2020 8:32 PM, Bhaumik Bhatt wrote:
    > While writing any sequence or session identifiers, it is possible that
    > the host could write a zero value, whereas only non-zero values should
    > be supported writes to those registers. Ensure that the host does not
    > write a non-zero value for them and also log them in debug messages.
    >
    > Suggested-by: Jeffrey Hugo <jhugo@codeaurora.org>
    > Signed-off-by: Bhaumik Bhatt <bbhatt@codeaurora.org>
    > ---
    > drivers/bus/mhi/core/boot.c | 15 +++++++--------
    > drivers/bus/mhi/core/internal.h | 1 +
    > 2 files changed, 8 insertions(+), 8 deletions(-)
    >
    > diff --git a/drivers/bus/mhi/core/boot.c b/drivers/bus/mhi/core/boot.c
    > index e5fcde1..9fe9c59 100644
    > --- a/drivers/bus/mhi/core/boot.c
    > +++ b/drivers/bus/mhi/core/boot.c
    > @@ -43,10 +43,7 @@ void mhi_rddm_prepare(struct mhi_controller *mhi_cntrl,
    > lower_32_bits(mhi_buf->dma_addr));
    >
    > mhi_write_reg(mhi_cntrl, base, BHIE_RXVECSIZE_OFFS, mhi_buf->len);
    > - sequence_id = prandom_u32() & BHIE_RXVECSTATUS_SEQNUM_BMSK;
    > -
    > - if (unlikely(!sequence_id))
    > - sequence_id = 1;
    > + sequence_id = (MHI_RANDOM_U32_NONZERO & BHIE_RXVECSTATUS_SEQNUM_BMSK);

    I don't think this math works. For example, if MHI_RANDOM_U32_NONZERO
    is 0x0FF0, and BHIE_RXVECSTATUS_SEQNUM_BMSK is 0xF, then sequence_id
    will end up being 0.

    --
    Jeffrey Hugo
    Qualcomm Technologies, Inc. is a member of the
    Code Aurora Forum, a Linux Foundation Collaborative Project.

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