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Date:   Wed, 30 Oct 2019 14:28:41 +0800
From:   zhichen@codeaurora.org
To:     Adrian Chadd <adrian@freebsd.org>
Cc:     Peter Oh <peter.oh@eero.com>, ath10k <ath10k@lists.infradead.org>,
        linux-wireless@vger.kernel.org
Subject: Re: [PATCH RFC] Revert "ath10k: fix DMA related firmware crashes on
 multiple devices"
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On 2019-10-23 02:24, Adrian Chadd wrote:
> On Tue, 22 Oct 2019 at 10:17, Peter Oh <peter.oh@eero.com> wrote:
>> 
>> 
>> On 10/22/19 1:57 AM, Zhi Chen wrote:
>> > This reverts commit 76d164f582150fd0259ec0fcbc485470bcd8033e.
>> > PCIe hung issue was observed on multiple platforms. The issue was reproduced
>> > when DUT was configured as AP and associated with 50+ STAs.
>> >
>> > With PCIe protocol analyzer, we can see DMA Read crossing 4KB boundary when
>> > issue happened. It broke PCIe spec and caused PCIe stuck.
>> 
>> How can you say value 0 (I believe it's 64 bytes) DMA burst size 
>> causes
>> the symptom and 1 fixes it?
> 
> 
> +1 to this question.
> 
> Also, shouldn't the DMA engine be doing what the firmware says? Is the
> firmware/copy engine actually somehow bursting / prefetching across a
> 4K page boundary?
> 
> Surely this is something that can be fixed in software/firmware by
> correctly configuring up buffer size/offsets?
> 
> 
> 
> -Adrian

DMA engine is working as expected as the configuration. It's copy engine 
which actually
splits the RD/WR requests and accesses host memory.
And yes it's platform related configuration. We have never hit this 
issue on x86 platform.


Zhi