linux-kernel - Re: [patch 2.6.27-rc3] at91_mci: don't use coherent dma buffers

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Date:	Thu, 21 Aug 2008 15:50:50 +0200
From:	Pierre Ossman <drzeus-mmc@...eus.cx>
To:	David Brownell <david-b@...bell.net>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Andrew Victor <linux@...im.org.za>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Russell King <rmk@....linux.org.uk>
Subject: Re: [patch 2.6.27-rc3] at91_mci: don't use coherent dma buffers

Ok with you nicolas?

On Mon, 18 Aug 2008 16:07:21 -0700
David Brownell <david-b@...bell.net> wrote:

> From: David Brownell <dbrownell@...rs.sourceforge.net>
> 
> At91_mci is abusing dma_free_coherent(), which may not be called
> with IRQs disabled.  I saw "mkfs.ext3" on an MMC card objecting
> voluminously as each write completed:
> 
>  WARNING: at arch/arm/mm/consistent.c:368 dma_free_coherent+0x2c/0x224()
>  [<c002726c>] (dump_stack+0x0/0x14) from [<c00387d4>] (warn_on_slowpath+0x4c/0x68)
>  [<c0038788>] (warn_on_slowpath+0x0/0x68) from [<c0028768>] (dma_free_coherent+0x2c/0x224)
>   r6:00008008 r5:ffc06000 r4:00000000
>  [<c002873c>] (dma_free_coherent+0x0/0x224) from [<c01918ac>] (at91_mci_irq+0x374/0x420)
>  [<c0191538>] (at91_mci_irq+0x0/0x420) from [<c0065d9c>] (handle_IRQ_event+0x2c/0x6c)
>  ...
> 
> This bug has been around for a LONG time.  The MM warning is
> from late 2005, but the driver merged a year later ... so I'm
> puzzled why nobody noticed this before now.
> 
> The fix involves noting that this buffer shouldn't be DMA-coherent;
> it's just used for normal DMA writes.  So replace it with standard
> kmalloc() buffering and DMA mapping calls.
> 
> This is the quickie fix.  A better one would not rely on allocating
> large bounce buffers.  (Note that dma_alloc_coherent could have failed
> too, but that case was ignored... kmalloc is a bit more likely to
> fail though.)
> 
> Signed-off-by: David Brownell <dbrownell@...rs.sourceforge.net>
> 
> ---
>  drivers/mmc/host/at91_mci.c |   20 ++++++++++++++++----
>  1 file changed, 16 insertions(+), 4 deletions(-)
> 
> --- a/drivers/mmc/host/at91_mci.c
> +++ b/drivers/mmc/host/at91_mci.c
> @@ -621,12 +621,21 @@ static void at91_mci_send_command(struct
>  				if (cpu_is_at91sam9260 () || cpu_is_at91sam9263())
>  					if (host->total_length < 12)
>  						host->total_length = 12;
> -				host->buffer = dma_alloc_coherent(NULL,
> -						host->total_length,
> -						&host->physical_address, GFP_KERNEL);
> +
> +				host->buffer = kmalloc(host->total_length, GFP_KERNEL);
> +				if (!host->buffer) {
> +					pr_debug("Can't alloc tx buffer\n");
> +					cmd->error = -ENOMEM;
> +					mmc_request_done(host->mmc, host->request);
> +					return;
> +				}
>  
>  				at91_mci_sg_to_dma(host, data);
>  
> +				host->physical_address = dma_map_single(NULL,
> +						host->buffer, host->total_length,
> +						DMA_TO_DEVICE);
> +
>  				pr_debug("Transmitting %d bytes\n", host->total_length);
>  
>  				at91_mci_write(host, ATMEL_PDC_TPR, host->physical_address);
> @@ -694,7 +703,10 @@ static void at91_mci_completed_command(s
>  	cmd->resp[3] = at91_mci_read(host, AT91_MCI_RSPR(3));
>  
>  	if (host->buffer) {
> -		dma_free_coherent(NULL, host->total_length, host->buffer, host->physical_address);
> +		dma_unmap_single(NULL,
> +				host->physical_address, host->total_length,
> +				DMA_TO_DEVICE);
> +		kfree(host->buffer);
>  		host->buffer = NULL;
>  	}
>  


-- 
     -- Pierre Ossman

  Linux kernel, MMC maintainer        http://www.kernel.org
  rdesktop, core developer          http://www.rdesktop.org

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