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From: Bjorn Helgaas <helgaas@kernel.org>
To: Muni Sekhar <munisekharrms@gmail.com>
Cc: linux-pci@vger.kernel.org, Christoph Hellwig <hch@lst.de>
Subject: Re: Question about pci_alloc_consistent() return address
Date: Thu, 14 Nov 2019 13:17:50 -0600	[thread overview]
Message-ID: <20191114191750.GA230106@google.com> (raw)
In-Reply-To: <CAHhAz+j+pN3fy_9NTBBchuz_X1a-FQK0Lt8ty3sk3qkufH7KYQ@mail.gmail.com>

[+cc Christoph]

On Thu, Nov 14, 2019 at 02:21:21PM +0530, Muni Sekhar wrote:
>  I’m using pci_alloc_consistent() in PCIe driver. My PCIe device only
> works 64 bit data  boundary transactions.
> 
> Is there a way to make sure pci_alloc_consistent() always returns
> 64-bit aligned address?

See Documentation/DMA-API-HOWTO.txt.  pci_alloc_consistent() is
implemented in terms of dma_alloc_coherent(), and that doc says
regions returned from dma_alloc_coherent() are guaranteed to be at
least PAGE_SIZE-aligned.

Are you seeing otherwise, or are you just making sure?  The dma_pool
interface for allocating smaller regions has a way to request the
alignment you need.

Bjorn

  reply	other threads:[~2019-11-14 19:17 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-14  8:51 Question about pci_alloc_consistent() return address Muni Sekhar
2019-11-14 19:17 ` Bjorn Helgaas [this message]
2019-11-16 18:36   ` Muni Sekhar

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