Subject: Re: [PATCH net-next 3/5] cassini: Remove unnecessary use of kmap_atomic()

From: "Fabio M. De Francesco" <[email-masked]>
Date: Fri, 18 Nov 2022 21:30:54 +0100

On venerdì 18 novembre 2022 18:55:36 CET Anirudh Venkataramanan wrote:
> On 11/18/2022 12:35 AM, Fabio M. De Francesco wrote:
> > On giovedì 17 novembre 2022 23:25:55 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.
> >> 
> >> I don't have hardware, so this change has only been compile tested.
> >> 
> >> Cc: Ira Weiny <[email-masked]>
> >> Cc: Fabio M. De Francesco <[email-masked]>
> >> Signed-off-by: Anirudh Venkataramanan <[email-masked]>
> >> ---
> >> 
> >>   drivers/net/ethernet/sun/cassini.c | 34 ++++++++++--------------------
> >>   1 file changed, 11 insertions(+), 23 deletions(-)
> >> 
> >> 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;
> >> 
> >> -		}
> >> +
> > 
> > This is a different logical change. Some maintainers I met would have 
asked
> > for a separate patch, but I'm OK with it being here.
> 
> cas_page_map()/cap_page_unmap() were using addr. Once these went away
> addr became unnecessary. It would be weird to leave the declaration,
> init and reinit for a variable that's not of any use, and so it was
> removed as well. It's cleaner this way.
> 
> Ani

Oh, sorry. You are right here. I didn't notice this connection. I probably 
took too little time to read your code carefully and interpreted those two 
lines another way :-(

Thanks,

Fabio