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Date: Fri, 25 Nov 2022 16:38:30 +0100
From: "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To: netdev@...r.kernel.org,
Anirudh Venkataramanan <anirudh.venkataramanan@...el.com>
Cc: Ira Weiny <ira.weiny@...el.com>,
Anirudh Venkataramanan <anirudh.venkataramanan@...el.com>
Subject: Re: [PATCH v2 net-next 3/6] cassini: Use page_address() instead of kmap_atomic()
On mercoledì 23 novembre 2022 21:52:16 CET Anirudh Venkataramanan wrote:
> Pages for Rx buffers are allocated in cas_page_alloc() using either
> GFP_ATOMIC or GFP_KERNEL. Memory allocated with GFP_KERNEL/GFP_ATOMIC can't
> come from highmem and so there's no need to kmap() them. Just use
> page_address() instead. This makes the variable 'addr' unnecessary, so
> remove it too.
>
> Note that kmap_atomic() disables preemption and page-fault processing,
> but page_address() doesn't. When removing uses of kmap_atomic(), one has to
> check if the code being executed between the map/unmap implicitly depends
> on page-faults and/or preemption being disabled. If yes, then code to
> disable page-faults and/or preemption should also be added for functional
> correctness. That however doesn't appear to be the case here, so just
> page_address() is used.
>
> I don't have hardware, so this change has only been compile tested.
>
> Cc: Ira Weiny <ira.weiny@...el.com>
> Cc: Fabio M. De Francesco <fmdefrancesco@...il.com>
> Signed-off-by: Anirudh Venkataramanan <anirudh.venkataramanan@...el.com>
> ---
> v1 -> v2: Update commit message
> ---
> drivers/net/ethernet/sun/cassini.c | 34 ++++++++++--------------------
> 1 file changed, 11 insertions(+), 23 deletions(-)
Reviewed-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
Thanks,
Fabio
> diff --git a/drivers/net/ethernet/sun/cassini.c
> b/drivers/net/ethernet/sun/cassini.c index 0aca193..2f66cfc 100644
> --- a/drivers/net/ethernet/sun/cassini.c
> +++ b/drivers/net/ethernet/sun/cassini.c
> @@ -1915,7 +1915,7 @@ static int cas_rx_process_pkt(struct cas *cp, struct
> cas_rx_comp *rxc, int off, swivel = RX_SWIVEL_OFF_VAL;
> struct cas_page *page;
> struct sk_buff *skb;
> - void *addr, *crcaddr;
> + void *crcaddr;
> __sum16 csum;
> char *p;
>
> @@ -1936,7 +1936,7 @@ static int cas_rx_process_pkt(struct cas *cp, struct
> cas_rx_comp *rxc, skb_reserve(skb, swivel);
>
> p = skb->data;
> - addr = crcaddr = NULL;
> + crcaddr = NULL;
> if (hlen) { /* always copy header pages */
> i = CAS_VAL(RX_COMP2_HDR_INDEX, words[1]);
> page = cp->rx_pages[CAS_VAL(RX_INDEX_RING, i)]
[CAS_VAL(RX_INDEX_NUM, i)];
> @@ -1948,12 +1948,10 @@ static int cas_rx_process_pkt(struct cas *cp, struct
> cas_rx_comp *rxc, i += cp->crc_size;
> dma_sync_single_for_cpu(&cp->pdev->dev, page->dma_addr +
off,
> i, DMA_FROM_DEVICE);
> - addr = cas_page_map(page->buffer);
> - memcpy(p, addr + off, i);
> + memcpy(p, page_address(page->buffer) + off, i);
> dma_sync_single_for_device(&cp->pdev->dev,
> page->dma_addr + off, i,
> DMA_FROM_DEVICE);
> - cas_page_unmap(addr);
> RX_USED_ADD(page, 0x100);
> p += hlen;
> swivel = 0;
> @@ -1984,12 +1982,11 @@ static int cas_rx_process_pkt(struct cas *cp, struct
> cas_rx_comp *rxc, /* make sure we always copy a header */
> swivel = 0;
> if (p == (char *) skb->data) { /* not split */
> - addr = cas_page_map(page->buffer);
> - memcpy(p, addr + off, RX_COPY_MIN);
> + memcpy(p, page_address(page->buffer) + off,
> + RX_COPY_MIN);
> dma_sync_single_for_device(&cp->pdev->dev,
> page->dma_addr
+ off, i,
>
DMA_FROM_DEVICE);
> - cas_page_unmap(addr);
> off += RX_COPY_MIN;
> swivel = RX_COPY_MIN;
> RX_USED_ADD(page, cp->mtu_stride);
> @@ -2036,10 +2033,8 @@ static int cas_rx_process_pkt(struct cas *cp, struct
> cas_rx_comp *rxc, RX_USED_ADD(page, hlen + cp->crc_size);
> }
>
> - if (cp->crc_size) {
> - addr = cas_page_map(page->buffer);
> - crcaddr = addr + off + hlen;
> - }
> + if (cp->crc_size)
> + crcaddr = page_address(page->buffer) + off +
hlen;
>
> } else {
> /* copying packet */
> @@ -2061,12 +2056,10 @@ static int cas_rx_process_pkt(struct cas *cp, struct
> cas_rx_comp *rxc, i += cp->crc_size;
> dma_sync_single_for_cpu(&cp->pdev->dev, page->dma_addr +
off,
> i, DMA_FROM_DEVICE);
> - addr = cas_page_map(page->buffer);
> - memcpy(p, addr + off, i);
> + memcpy(p, page_address(page->buffer) + off, i);
> dma_sync_single_for_device(&cp->pdev->dev,
> page->dma_addr + off, i,
> DMA_FROM_DEVICE);
> - cas_page_unmap(addr);
> if (p == (char *) skb->data) /* not split */
> RX_USED_ADD(page, cp->mtu_stride);
> else
> @@ -2081,20 +2074,17 @@ static int cas_rx_process_pkt(struct cas *cp, struct
> cas_rx_comp *rxc, page->dma_addr,
> dlen + cp-
>crc_size,
> DMA_FROM_DEVICE);
> - addr = cas_page_map(page->buffer);
> - memcpy(p, addr, dlen + cp->crc_size);
> + memcpy(p, page_address(page->buffer), dlen + cp-
>crc_size);
> dma_sync_single_for_device(&cp->pdev->dev,
> page->dma_addr,
> dlen + cp-
>crc_size,
>
DMA_FROM_DEVICE);
> - cas_page_unmap(addr);
> RX_USED_ADD(page, dlen + cp->crc_size);
> }
> end_copy_pkt:
> - if (cp->crc_size) {
> - addr = NULL;
> + if (cp->crc_size)
> crcaddr = skb->data + alloclen;
> - }
> +
> skb_put(skb, alloclen);
> }
>
> @@ -2103,8 +2093,6 @@ static int cas_rx_process_pkt(struct cas *cp, struct
> cas_rx_comp *rxc, /* checksum includes FCS. strip it out. */
> csum = csum_fold(csum_partial(crcaddr, cp->crc_size,
> csum_unfold(csum)));
> - if (addr)
> - cas_page_unmap(addr);
> }
> skb->protocol = eth_type_trans(skb, cp->dev);
> if (skb->protocol == htons(ETH_P_IP)) {
> --
> 2.37.2
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