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

[Nobuhiro Iwamatsu]

Hi!

I comment to latest patch.

Best regards,
  Nobuhiro

2014-11-13 1:23 GMT+09:00 Simon Glass <sjg at chromium.org>:
> 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



-- 
Nobuhiro Iwamatsu
   iwamatsu at {nigauri.org / debian.org}
   GPG ID: 40AD1FA6