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From:   Kalle Valo <kvalo@codeaurora.org>
To:     Ben Greear <greearb@candelatech.com>
Cc:     linux-wireless@vger.kernel.org
Subject: Re: [PATCH] ath10k: Free beacon buf later in vdev teardown.
References: <20190227162756.13048-1-greearb@candelatech.com>
        <20190910131244.267AF602F2@smtp.codeaurora.org>
        <89712e32-1fb2-f002-15ed-046871c161ce@candelatech.com>
Date:   Thu, 12 Sep 2019 15:47:35 +0300
In-Reply-To: <89712e32-1fb2-f002-15ed-046871c161ce@candelatech.com> (Ben
        Greear's message of "Tue, 10 Sep 2019 06:19:35 -0700")
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Ben Greear <greearb@candelatech.com> writes:

> On 09/10/2019 06:12 AM, Kalle Valo wrote:
>> greearb@candelatech.com wrote:
>>
>>> My wave-1 firmware often crashes when I am bringing down
>>> AP vdevs, and sometimes at least some machines lockup hard
>>> after spewing IOMMU errors.
>>>
>>> I don't see the same issue in STA mode, so I suspect beacons
>>> are the issue.
>>>
>>> Moving the beacon buf deletion to later in the vdev teardown
>>> logic appears to help this problem.  Firmware still crashes
>>> often, but several iterations did not show IOMMU errors and
>>> machine didn't hang.
>>
>> I'm not really fond of fixing issues just by luck but after a quick look at the
>> code I can't see any harm in this change either. So I guess it's ok.
>>
>> But can you provide the exact hardware and firmware you used for testing, I'll
>> add it to the commit log. I want to document that in every commit:
>
> I used Compex WLE900VX hardware, and the firmware was ath10k-ct something or other,
> it has been a long time, so I don't recall the exact firmware version.

Ok, I added QCA9880 and unspecified version of ath10k-ct firmware to the
commit log.

> The real fix for this is to have the firmware do proper beacon tx
> completion logic so that the driver can know when it can safely free
> buffers. I implemented this in my ath10k-ct firmware/driver, but
> unless you want to start accepting patches for my firmware, then that
> will not help upstream ath10k.

It's a challenge enough to support so many differerent QCOM firmware
branches and still try to avoid bloating the driver too much to keep it
maintainable. Adding support for a new firmware branch/fork with a
significantly different interface would make everything so much harder.

-- 
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