linux-kernel - Re: [RFC PATCH] net: macb: Apply RXUBR workaround only to versions with errata

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Message-ID: <fbd59625-b36b-76f3-6f88-78efe901f67a@microchip.com>
Date:   Thu, 29 Nov 2018 10:43:41 +0000
From:   <Claudiu.Beznea@...rochip.com>
To:     <harinik@...inx.com>
CC:     <harini.katakam@...inx.com>, <Nicolas.Ferre@...rochip.com>,
        <davem@...emloft.net>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <michal.simek@...inx.com>
Subject: Re: [RFC PATCH] net: macb: Apply RXUBR workaround only to versions
 with errata



On 29.11.2018 12:38, Harini Katakam wrote:
> Hi Claudiu,
> On Thu, Nov 29, 2018 at 3:51 PM <Claudiu.Beznea@...rochip.com> wrote:
>>
>>
>>
>> On 23.11.2018 11:59, Harini Katakam wrote:
> <snip>
>>> -             if (status & MACB_BIT(RXUBR)) {
>>> +             if ((bp->errata & MACB_ERRATA_RXLOCKUP) &&
>>> +                 (status & MACB_BIT(RXUBR))) {
>>
>> Just asking, did you manage to test this on other platforms that haven't
>> this issue?
>> SAMA5D2 datasheet [1] states this:
>> "When in packet buffer full store and forward mode, only good received
>> frames are written out of the DMA, so no
>>  fragments will exist in the AHB buffers due to MAC receiver errors. There
>> is still the possibility of fragments due to
>>  DMA errors, for example used bit read on the second buffer of a
>> multibuffer frame."
>>
>> But it is true that nowhere is presented that this must be special treated.
>>
> 
> Yes, I tested it on ZynqMP which does NOT have this errata - did perf and
> ping flood and dint see any issues.

Great! Thank you, Harini!

> Just FYI, the errata in the IP version in Zynq causes an RX lock up under
> high stress (when there is obviously multiple RXUBR interrupts). The RX reset
> is a pre-emptive workaround to *mostly* avoid the issue.
> Please see Answer record 52028 in
> https://www.xilinx.com/support/documentation/errata/en247.pdf
> 
>> Moreover, if you do this only for MACB_ERRATA_RXLOCKUP and still have RXUBR
>> interrupt enabled every time it would not make sense to still enable it.
>> Or, if you want it enabled every time, you should clear it no matter the
>> MACB_ERRATA_RXLOCKUP is set or not, with something like this:
>>
>>                         if (bp->caps & MACB_CAPS_ISR_CLEAR_ON_WRITE)
>>
>>                                 queue_writel(queue, ISR, MACB_BIT(RXUBR));
>>
>>
> Thanks for pointing this out - yes i'll move the WTC code outside the check.
> 
> Regards,
> Harini
>