* Question about pci_alloc_consistent() return address
@ 2019-11-14 8:51 Muni Sekhar
2019-11-14 19:17 ` Bjorn Helgaas
0 siblings, 1 reply; 3+ messages in thread
From: Muni Sekhar @ 2019-11-14 8:51 UTC (permalink / raw)
To: linux-pci
Hi All,
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?
--
Thanks,
Sekhar
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Question about pci_alloc_consistent() return address
2019-11-14 8:51 Question about pci_alloc_consistent() return address Muni Sekhar
@ 2019-11-14 19:17 ` Bjorn Helgaas
2019-11-16 18:36 ` Muni Sekhar
0 siblings, 1 reply; 3+ messages in thread
From: Bjorn Helgaas @ 2019-11-14 19:17 UTC (permalink / raw)
To: Muni Sekhar; +Cc: linux-pci, Christoph Hellwig
[+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
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Question about pci_alloc_consistent() return address
2019-11-14 19:17 ` Bjorn Helgaas
@ 2019-11-16 18:36 ` Muni Sekhar
0 siblings, 0 replies; 3+ messages in thread
From: Muni Sekhar @ 2019-11-16 18:36 UTC (permalink / raw)
To: Bjorn Helgaas; +Cc: linux-pci, Christoph Hellwig
On Fri, Nov 15, 2019 at 12:47 AM Bjorn Helgaas <helgaas@kernel.org> wrote:
>
> [+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.
Thanks for the clarification. I just want to make sure that
pci_alloc_consistent() returns 64-bit aligned address.
>
> Bjorn
--
Thanks,
Sekhar
^ permalink raw reply [flat|nested] 3+ messages in thread
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