netdev - Re: [PATCH] net/macb: Use non-coherent memory for rx buffers

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Date:	Fri, 23 Nov 2012 17:12:21 +0100
From:	Joachim Eastwood <manabian@...il.com>
To:	Nicolas Ferre <nicolas.ferre@...el.com>
Cc:	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>,
	Havard Skinnemoen <havard@...nnemoen.net>
Subject: Re: [PATCH] net/macb: Use non-coherent memory for rx buffers

Hi Nicolas,

On 23 November 2012 14:50, Nicolas Ferre <nicolas.ferre@...el.com> wrote:
> From: Havard Skinnemoen <havard@...nnemoen.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@...nnemoen.net>
> [nicolas.ferre@...el.com: adapt to newer kernel]
> Signed-off-by: Nicolas Ferre <nicolas.ferre@...el.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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