Question about pci_alloc_consistent() return address

Question about pci_alloc_consistent() return address

[Muni Sekhar]

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

Re: Question about pci_alloc_consistent() return address

[Bjorn Helgaas]

[+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

Re: Question about pci_alloc_consistent() return address

[Muni Sekhar]

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