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From: Matthieu CASTET <matthieu.castet@parrot.com>
To: "video4linux-list@redhat.com" <video4linux-list@redhat.com>
Cc: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Subject: videobuf-dma-contig sync question
Date: Wed, 22 Apr 2009 11:50:02 +0200	[thread overview]
Message-ID: <49EEE84A.5090400@parrot.com> (raw)

Hi,


I don't understand why __videobuf_sync in videobuf-dma-contig isn't a nop.

All the memory allocated by videobuf-dma-contig is coherent memory. And
Documentation/DMA-API.txt seems to imply that this memory is coherent
and doesn't need extra cache operation for synchronization.

Also calling dma_sync_single_for_cpu cause panic on arm for per-device
coherent memory, because the memory isn't in the main memory[1].

Why __videobuf_sync need dma_sync_single_for_cpu ?

Regards,

Matthieu



[1]
void dma_cache_maint(const void *start, size_t size, int direction)
{
    const void *end = start + size;

    BUG_ON(!virt_addr_valid(start) || !virt_addr_valid(end - 1));

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             reply	other threads:[~2009-04-22  9:50 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-04-22  9:50 Matthieu CASTET [this message]
2009-04-22 11:31 ` videobuf-dma-contig sync question Magnus Damm
2009-04-23  3:45   ` Paul Mundt

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