linux-kernel - Re: [Question] Missing data after DMA read transfer

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Message-ID: <278aff83-5d3a-e755-a4c3-50bfccf08886@kalray.eu>
Date:	Thu, 21 Apr 2016 10:51:52 +0200
From:	Nicolas Morey-Chaisemartin <nmorey@...ray.eu>
To:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [Question] Missing data after DMA read transfer



Le 04/21/2016 à 10:35 AM, One Thousand Gnomes a écrit :
>> But if I try to copy_from_user (using the address coming from userland, the one passed to get_user_pages), the data has not been written and I see the memset value.
>>
>> I manage to build a test case that fails all the time, but never at the same offset within the buffer.
>> It's always in the middle (never at the start nor end), for a few pages long (varies between runs).
> Always page aligned, always cache line aligned or arbitrarily aligned ?
>
> Alan
It's always page aligned for both start and end (meaning last "untransferred" byte is the last byte of a page)

Nicolas