[U-Boot] [PATCH] net: fec_mxc: Fix timeouts during tftp transfer

[Marek Vasut <marex@denx.de>]

Dear Fabio Estevam,

> From: Fabio Estevam <fabio.estevam@freescale.com>
> 
> Performing tftp transfers on mx28 results in random timeouts.
> 
> Hector Palacios and Robert Hodaszi analyzed the root cause being related to
> the alignment of the 'buff' buffer inside fec_recv().
> 
> GCC versions such as 4.4/4.5 are more likely to exhibit such problem.
> 
> Use ALLOC_CACHE_ALIGN_BUFFER() for making the proper alignment of buffer.
> 
> Reported-by: Hector Palacios <hector.palacios@digi.com>
> Tested-by: Oliver Metz <oliver@freetz.org>
> Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
> ---
>  drivers/net/fec_mxc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/fec_mxc.c b/drivers/net/fec_mxc.c
> index 690e572..b423ff6 100644
> --- a/drivers/net/fec_mxc.c
> +++ b/drivers/net/fec_mxc.c
> @@ -794,7 +794,7 @@ static int fec_recv(struct eth_device *dev)
>  	uint16_t bd_status;
>  	uint32_t addr, size, end;
>  	int i;
> -	uchar buff[FEC_MAX_PKT_SIZE] __aligned(ARCH_DMA_MINALIGN);
> +	ALLOC_CACHE_ALIGN_BUFFER(uchar, buff, FEC_MAX_PKT_SIZE);

OK, it's gonna be safer this way, still what's the root cause of the issue?

FEC_MAX_PKT_SIZE is 1536 (which is aligned to 32b and even 64b)
__aligned(ARCH_DMA_MINALIGN) aligns the stuff to 32b or 64b depending on CPU

So how can the above not properly align the buffer? Is that a compiler bug then?

btw. using ALLOC_CACHE_ALIGN_BUFFER will be safer were someone to change 
FEC_MAX_PKT_SIZE, the buffer would still be safe for cache flush/inval ops.

Best regards,
Marek Vasut