linux-kernel - Re: [PATCH] firewire: fw-ohci: use dma_alloc_coherent for ar

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Date:	Thu, 13 Mar 2008 00:30:34 +0100
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	Jarod Wilson <jwilson@...hat.com>
CC:	linux1394-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org,
	Kristian Høgsberg <krh@...planet.net>
Subject: Re: [PATCH] firewire: fw-ohci: use dma_alloc_coherent for ar_buffer

Jarod Wilson wrote:
> Currently, we do nothing to guarantee we have a consistent DMA buffer for
> asynchronous receive packets. Rather than doing several sync's following a
> dma_map_single() to get consistent buffers, just switch to using
> dma_alloc_coherent().
> 
> Resolves constant buffer failures on my own x86_64 laptop w/4GB of RAM and
> likely to fix a number of other failures witnessed on x86_64 systems with
> 4GB of RAM or more.
> 
> Signed-off-by: Jarod Wilson <jwilson@...hat.com>

Looks good at first glance.  Alas my PCs aren't affected, so I can only 
test it for lack of regressions.

I'm tempted to push this to Linus later this week.  Unless e.g. Kristian 
has reservations.

> 
> ---
> 
>  drivers/firewire/fw-ohci.c |   18 +++++-------------
>  1 files changed, 5 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/firewire/fw-ohci.c b/drivers/firewire/fw-ohci.c
> index 28ea78c..081a434 100644
> --- a/drivers/firewire/fw-ohci.c
> +++ b/drivers/firewire/fw-ohci.c
> @@ -284,16 +284,10 @@ static int ar_context_add_page(struct ar_context *ctx)
>  	dma_addr_t ab_bus;
>  	size_t offset;
>  
> -	ab = (struct ar_buffer *) __get_free_page(GFP_ATOMIC);
> +	ab = dma_alloc_coherent(dev, PAGE_SIZE, &ab_bus, GFP_ATOMIC);
>  	if (ab == NULL)
>  		return -ENOMEM;
>  
> -	ab_bus = dma_map_single(dev, ab, PAGE_SIZE, DMA_BIDIRECTIONAL);
> -	if (dma_mapping_error(ab_bus)) {
> -		free_page((unsigned long) ab);
> -		return -ENOMEM;
> -	}
> -
>  	memset(&ab->descriptor, 0, sizeof(ab->descriptor));
>  	ab->descriptor.control        = cpu_to_le16(DESCRIPTOR_INPUT_MORE |
>  						    DESCRIPTOR_STATUS |
> @@ -304,8 +298,6 @@ static int ar_context_add_page(struct ar_context *ctx)
>  	ab->descriptor.res_count      = cpu_to_le16(PAGE_SIZE - offset);
>  	ab->descriptor.branch_address = 0;
>  
> -	dma_sync_single_for_device(dev, ab_bus, PAGE_SIZE, DMA_BIDIRECTIONAL);
> -
>  	ctx->last_buffer->descriptor.branch_address = cpu_to_le32(ab_bus | 1);
>  	ctx->last_buffer->next = ab;
>  	ctx->last_buffer = ab;
> @@ -409,6 +401,7 @@ static void ar_context_tasklet(unsigned long data)
>  
>  	if (d->res_count == 0) {
>  		size_t size, rest, offset;
> +		dma_addr_t buffer_bus;
>  
>  		/*
>  		 * This descriptor is finished and we may have a
> @@ -417,9 +410,7 @@ static void ar_context_tasklet(unsigned long data)
>  		 */
>  
>  		offset = offsetof(struct ar_buffer, data);
> -		dma_unmap_single(ohci->card.device,
> -			le32_to_cpu(ab->descriptor.data_address) - offset,
> -			PAGE_SIZE, DMA_BIDIRECTIONAL);
> +		buffer_bus = le32_to_cpu(ab->descriptor.data_address) - offset;
>  
>  		buffer = ab;
>  		ab = ab->next;
> @@ -435,7 +426,8 @@ static void ar_context_tasklet(unsigned long data)
>  		while (buffer < end)
>  			buffer = handle_ar_packet(ctx, buffer);
>  
> -		free_page((unsigned long)buffer);
> +		dma_free_coherent(ohci->card.device, PAGE_SIZE,
> +				  buffer, buffer_bus);
>  		ar_context_add_page(ctx);
>  	} else {
>  		buffer = ctx->pointer;
> 


-- 
Stefan Richter
-=====-==--- --== -==-=
http://arcgraph.de/sr/
--
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