[U-Boot] [PATCH 7/9] net: rtl8169: Properly align buffers

[Thierry Reding <thierry.reding@gmail.com>]

On Wed, Aug 20, 2014 at 01:29:57PM -0600, Stephen Warren wrote:
> On 08/18/2014 02:00 AM, Thierry Reding wrote:
> >From: Thierry Reding <treding@nvidia.com>
> >
> >RX and TX descriptor rings should be aligned to 256 byte boundaries. Use
> >the DEFINE_ALIGN_BUFFER() macro to define the buffers so that they don't
> >have to be manually aligned later on. Also make sure that the buffers do
> >align to cache-line boundaries in case the cache-line is higher than the
> >256 byte alignment requirements of the NIC.
> >
> >Also add a warning if the cache-line size is larger than the descriptor
> >size, because the driver may discard changes to descriptors made by the
> >hardware when requeuing RX buffers.
> 
> >@@ -909,6 +899,18 @@ static int rtl_init(struct eth_device *dev, bd_t *bis)
> 
> >+	/*
> >+	 * Warn if the cache-line size is larger than the descriptor size. In
> >+	 * such cases the driver will likely fail because the CPU needs to
> >+	 * flush the cache when requeuing RX buffers, therefore descriptors
> >+	 * written by the hardware may be discarded.
> >+	 */
> >+	if (ARCH_DMA_MINALIGN > sizeof(struct RxDesc))
> >+		printf("WARNING: cache-line size is larger than descriptor size\n");
> 
> I'd be tempted to make that a compile-time #error (or perhaps just a
> #warning) Perhaps #error would break compilation of existing boards though?

There are two SH4 boards that use the rtl8169 (r7780mp and sh7785lcr)
for which this condition is true, so #error would break them (well,
technically not r7780mp since it comments out CONFIG_RTL8169 in the
configuration). I'll make it a #warning instead.

Thierry
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