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

[Simon Glass]

On 22 August 2014 03:15, Thierry Reding <thierry.reding at gmail.com> wrote:
> 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 at 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.

Adding the maintainer for comment.

Regards,
Simon