[PATCH] usb: musb: host: Issue a memory barrier before staring the DMA

[Sergei Shtylyov]

Hello.

Santosh Shilimkar wrote:

> This patch fixes the issue which was observed while transfering
> a large file ( > 20MB) over USB (OMAP MUSB controller acts as USB host)
> to an attached USB thumb drive.

> It was found that CDB field of CBW packet was set to 0x0. This was
> due to missing a barrier before DMA engine starts transfer.
> This  buffer is  allocated using dma_alloc_coherent which gives
> non-cacheble but bufferable memory and hence needed a write
> memory barrier to flush the write buffer.

> More info on this thread is here:
> 	http://www.spinics.net/lists/linux-omap/msg33987.html

> Signed-off-by: Maulik Mankad <x0082077 at ti.com>
> Signed-off-by: Santosh Shilimkar <santosh.shilimkar at ti.com>
> Cc: Russell King <rmk+kernel at arm.linux.org.uk>
> Cc: Felipe Balbi <felipebalbi at users.sourceforge.net>
> ---
>  drivers/usb/musb/musb_host.c |    6 ++++++
>  1 files changed, 6 insertions(+), 0 deletions(-)

> Index: omap4_integration/drivers/usb/musb/musb_host.c
> ===================================================================
> --- omap4_integration.orig/drivers/usb/musb/musb_host.c
> +++ omap4_integration/drivers/usb/musb/musb_host.c
> @@ -628,6 +628,11 @@ static bool musb_tx_dma_program(struct d
>  	u8			mode;
>  
>  #ifdef	CONFIG_USB_INVENTRA_DMA
> +	/*
> +	 * Ensure the data reaches to main memory before starting
> +	 * DMA transfer
> +	 */
> +	wmb();

    Are you sure this is only needed for Inventra DMA?

WBR, Sergei