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

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Message-ID: <20160421093512.4a63e2c2@lxorguk.ukuu.org.uk>
Date:	Thu, 21 Apr 2016 09:35:12 +0100
From:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:	Nicolas Morey-Chaisemartin <nmorey@...ray.eu>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [Question] Missing data after DMA read transfer

> 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