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SubjectRe: [PATCH v4 8/8] bus: mhi: core: Ensure non-zero session or sequence ID values are used
On 2020-05-04 07:33, Jeffrey Hugo wrote:
> 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.

In this case, SEQNUM BMSK is set to 0x3FFFFFFF so this change will still
work as
we only supplied a non-zero number macro to AND with the mask.
However, I agree that may not be the case always that we would know the
bitmask
in advance so it is better to fix it for good.

Thanks for the catch! I have updated the change to have the macro take
the
bitmask as a parameter and output a non-zero value.

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