On Thu, Mar 26, 2015 at 01:06:31PM +0000, Ben Dooks wrote:
> Always write the descriptors for the at_xdmac in little endian when
> the processor is running big endian.
>
> Signed-off-by: Ben Dooks <ben.dooks@xxxxxxxxxxxxxxx>
> --
> CC: Ludovic Desroches <ludovic.desroches@xxxxxxxxx>
> CC: Vinod Koul <vinod.koul@xxxxxxxxx>
> CC: Dan Williams <dan.j.williams@xxxxxxxxx>
> CC: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> CC: dmaengine@xxxxxxxxxxxxxxx
> ---
> drivers/dma/at_xdmac.c | 97 ++++++++++++++++++++++++++------------------------
> 1 file changed, 51 insertions(+), 46 deletions(-)
>
> diff --git a/drivers/dma/at_xdmac.c b/drivers/dma/at_xdmac.c
> index d9891d3..65a37be 100644
> --- a/drivers/dma/at_xdmac.c
> +++ b/drivers/dma/at_xdmac.c
> @@ -232,10 +232,10 @@ struct at_xdmac {
> /* Linked List Descriptor */
> struct at_xdmac_lld {
> dma_addr_t mbr_nda; /* Next Descriptor Member */
> - u32 mbr_ubc; /* Microblock Control Member */
> + __le32 mbr_ubc; /* Microblock Control Member */
> dma_addr_t mbr_sa; /* Source Address Member */
> dma_addr_t mbr_da; /* Destination Address Member */
> - u32 mbr_cfg; /* Configuration Register */
> + __le32 mbr_cfg; /* Configuration Register */
> };
This /really/ is not correct if this structure is describing something
parsed by the hardware - I mean, your patch itself may be correct
but it's showing that there's more problems here.
The reason is those dma_addr_t's. dma_addr_t can be either 32-bit or
64-bit depending on the kernel configuration, and I really suspect that
the hardware doesn't get to know how the kernel was configured. That
goes for any structure which is passed to hardware - dma_addr_t should
never appear in it _anywhere_.
As you're converting it to __le32, I suspec those DMA addresses are
also supposed to be __le32 quantities as well.
> + desc->lld.mbr_sa = cpu_to_le32(atchan->per_src_addr);
> + desc->lld.mbr_da = cpu_to_le32(mem);
This kind'a confirms it - but what happens to the above if dma_addr_t
is 64-bit and has some high bits set? Should be silently truncate the
value?
> dev_dbg(chan2dev(chan),
> "%s: lld: mbr_sa=%pad, mbr_da=%pad, mbr_ubc=0x%08x\n",
> __func__, &desc->lld.mbr_sa, &desc->lld.mbr_da, desc->lld.mbr_ubc);
>
> /* Chain lld. */
> if (prev) {
> - prev->lld.mbr_nda = desc->tx_dma_desc.phys;
> + prev->lld.mbr_nda = cpu_to_le32(desc->tx_dma_desc.phys);
Another point to be raised with the original authors... get rid of this
"phys" notation. It's not physical. It's an address which is specific
to the DMA controller, but which _may_ happen to be the same as a
physical address.
--
FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up
according to speedtest.net.
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