netdev - Re: [PATCH net-next 3/5] cassini: Remove unnecessary use of kmap

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Message-ID: <d9a3d57b-e72c-8f8f-b4ae-979836d87d32@intel.com>
Date:   Fri, 18 Nov 2022 09:55:36 -0800
From:   Anirudh Venkataramanan <anirudh.venkataramanan@...el.com>
To:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>,
        <netdev@...r.kernel.org>
CC:     Ira Weiny <ira.weiny@...el.com>
Subject: Re: [PATCH net-next 3/5] cassini: Remove unnecessary use of
 kmap_atomic()

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 <ira.weiny@...el.com>
>> Cc: Fabio M. De Francesco <fmdefrancesco@...il.com>
>> Signed-off-by: Anirudh Venkataramanan <anirudh.venkataramanan@...el.com>
>> ---
>>   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