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SubjectRe: [PATCH] net/macb: Use non-coherent memory for rx buffers
From
Hi Nicolas,

On 23 November 2012 14:50, Nicolas Ferre <nicolas.ferre@atmel.com> wrote:
> From: Havard Skinnemoen <havard@skinnemoen.net>
>
> Allocate regular pages to use as backing for the RX ring and use the
> DMA API to sync the caches. This should give a bit better performance
> since it allows the CPU to do burst transfers from memory. It is also
> a necessary step on the way to reduce the amount of copying done by
> the driver.
>
> Signed-off-by: Havard Skinnemoen <havard@skinnemoen.net>
> [nicolas.ferre@atmel.com: adapt to newer kernel]
> Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
> ---
> drivers/net/ethernet/cadence/macb.c | 206 +++++++++++++++++++++++-------------
> drivers/net/ethernet/cadence/macb.h | 20 +++-
> 2 files changed, 148 insertions(+), 78 deletions(-)

<snip>

> diff --git a/drivers/net/ethernet/cadence/macb.h b/drivers/net/ethernet/cadence/macb.h
> index 570908b..74e68a3 100644
> --- a/drivers/net/ethernet/cadence/macb.h
> +++ b/drivers/net/ethernet/cadence/macb.h
> @@ -453,6 +453,23 @@ struct macb_dma_desc {
> #define MACB_TX_USED_SIZE 1
>
> /**
> + * struct macb_rx_page - data associated with a page used as RX buffers
> + * @page: Physical page used as storage for the buffers
> + * @phys: DMA address of the page
> + *
> + * Each page is used to provide %MACB_RX_BUFFERS_PER_PAGE RX buffers.
> + * The page gets an initial reference when it is inserted into the
> + * ring, and an additional reference each time it is passed up the
> + * stack as a fragment. When all the buffers have been used, we drop
> + * the initial reference and allocate a new page. Any additional
> + * references are dropped when the higher layers free the skb.
> + */
> +struct macb_rx_page {
> + struct page *page;
> + dma_addr_t phys;
> +};
> +
> +/**
> * struct macb_tx_skb - data about an skb which is being transmitted
> * @skb: skb currently being transmitted
> * @mapping: DMA address of the skb's data buffer
> @@ -543,7 +560,7 @@ struct macb {
>
> unsigned int rx_tail;
> struct macb_dma_desc *rx_ring;
> - void *rx_buffers;
> + struct macb_rx_page *rx_page;
>
> unsigned int tx_head, tx_tail;
> struct macb_dma_desc *tx_ring;
> @@ -564,7 +581,6 @@ struct macb {
>
> dma_addr_t rx_ring_dma;
> dma_addr_t tx_ring_dma;
> - dma_addr_t rx_buffers_dma;
>
> struct mii_bus *mii_bus;
> struct phy_device *phy_dev;
> --

struct macb is shared between at91_ether and macb. Removing
rx_buffers_dma and rx_buffers will break compilation on at91_ether.

So please either leave the two struct members alone, for now, or fix
up at91_ether at the same time.

regards
Joachim Eastwood


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