netdev - Re: [PATCH net-next 3/3] net: stmmac: Introducing support for Page Pool

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Date:   Tue, 23 Jul 2019 14:34:21 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Jose Abreu <Jose.Abreu@...opsys.com>, Lars Persson <lists@...h.nu>,
        "Ilias Apalodimas" <ilias.apalodimas@...aro.org>
CC:     Joao Pinto <Joao.Pinto@...opsys.com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-stm32@...md-mailman.stormreply.com" 
        <linux-stm32@...md-mailman.stormreply.com>,
        Chen-Yu Tsai <wens@...e.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        linux-tegra <linux-tegra@...r.kernel.org>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        "David S . Miller" <davem@...emloft.net>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH net-next 3/3] net: stmmac: Introducing support for Page
 Pool


On 23/07/2019 13:51, Jose Abreu wrote:
> From: Jon Hunter <jonathanh@...dia.com>
> Date: Jul/23/2019, 12:58:55 (UTC+00:00)
> 
>>
>> On 23/07/2019 11:49, Jose Abreu wrote:
>>> From: Jon Hunter <jonathanh@...dia.com>
>>> Date: Jul/23/2019, 11:38:33 (UTC+00:00)
>>>
>>>>
>>>> On 23/07/2019 11:07, Jose Abreu wrote:
>>>>> From: Jon Hunter <jonathanh@...dia.com>
>>>>> Date: Jul/23/2019, 11:01:24 (UTC+00:00)
>>>>>
>>>>>> This appears to be a winner and by disabling the SMMU for the ethernet
>>>>>> controller and reverting commit 954a03be033c7cef80ddc232e7cbdb17df735663
>>>>>> this worked! So yes appears to be related to the SMMU being enabled. We
>>>>>> had to enable the SMMU for ethernet recently due to commit
>>>>>> 954a03be033c7cef80ddc232e7cbdb17df735663.
>>>>>
>>>>> Finally :)
>>>>>
>>>>> However, from "git show 954a03be033c7cef80ddc232e7cbdb17df735663":
>>>>>
>>>>> +         There are few reasons to allow unmatched stream bypass, and
>>>>> +         even fewer good ones.  If saying YES here breaks your board
>>>>> +         you should work on fixing your board.
>>>>>
>>>>> So, how can we fix this ? Is your ethernet DT node marked as 
>>>>> "dma-coherent;" ?
>>>>
>>>> TBH I have no idea. I can't say I fully understand your change or how it
>>>> is breaking things for us.
>>>>
>>>> Currently, the Tegra DT binding does not have 'dma-coherent' set. I see
>>>> this is optional, but I am not sure how you determine whether or not
>>>> this should be set.
>>>
>>> From my understanding it means that your device / IP DMA accesses are coherent regarding the CPU point of view. I think it will be the case if GMAC is not behind any kind of IOMMU in the HW arch.
>>
>> I understand what coherency is, I just don't know how you tell if this
>> implementation of the ethernet controller is coherent or not.
> 
> Do you have any detailed diagram of your HW ? Such as blocks / IPs 
> connection, address space wiring , ...

Yes, this can be found in the Tegra X2 Technical Reference Manual [0].
Unfortunately, you need to create an account to download it.

Jon

[0] https://developer.nvidia.com/embedded/dlc/parker-series-trm

-- 
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