linux-kernel - Re: [RFC 0/2] ath10k:set tx credit to one and delay the unmaping

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Date:   Fri, 21 Jan 2022 14:42:11 -0800
From:   Doug Anderson <dianders@...omium.org>
To:     Youghandhar Chintala <quic_youghand@...cinc.com>
Cc:     ath10k <ath10k@...ts.infradead.org>,
        linux-wireless <linux-wireless@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, quic_pillair@...cinc.com,
        Abhishek Kumar <kuabhs@...omium.org>,
        Brian Norris <briannorris@...omium.org>
Subject: Re: [RFC 0/2] ath10k:set tx credit to one and delay the unmaping

Hi,

On Thu, Jan 20, 2022 at 10:44 PM Youghandhar Chintala
<quic_youghand@...cinc.com> wrote:
>
> Currently for WCN3990, the host driver can send two wmi commands at once,
> now it is limiting to one because if HOST wants to initiate 2 DMA transfers,
> it is possible when copy complete interrupt for first DMA reaches HOST,
> CE has already updated SRRI for both DMA transfers and is in the middle
> of 2nd DMA. HOST uses SRRI to interpret how many DMA’s have been completed
> and tries to unmap/free both the DMA entries, but CE is still in the middle
> of 2nd DMA which can cause SMMU issues or corruption.
>
> We are seeing a corner case smmu fault issue where copy engine is still accessing
> the memory though host unmaps it hence as work around we are delaying the
> unmapping the memory and tx credit to one.
>
> Youghandhar Chintala (2):
>   ath10k: Set tx credit to one for wcn3990 snoc based devices
>   ath10k: Delay the unmapping of the buffer
>
>  drivers/net/wireless/ath/ath10k/core.c | 30 ++++++++++++++++++++++++++
>  drivers/net/wireless/ath/ath10k/htc.c  | 18 +++++++++++++---
>  drivers/net/wireless/ath/ath10k/htc.h  |  1 +
>  drivers/net/wireless/ath/ath10k/hw.h   |  6 ++++++
>  4 files changed, 52 insertions(+), 3 deletions(-)

I don't understand the root cause here myself. I also don't have
enough skin in the game to say whether this is the best/cleanest way
to work around the problem. Thus I'll refrain from a Reviewed-by tag.
That being said, I did a bunch of testing of this solution and I also
am aware of others that have tested it. Thus I'm convinced that it at
least works around the problem that has been observed. Hence:

Tested-by: Douglas Anderson <dianders@...omium.org>

In my case I was on the same (or nearly the same) hardware as
Youghandhar, though I had a slightly older build. FWIW:

Tested-on: WLAN.HL.3.2.2.c10-00754-QCAHLSWMTPL-1

-Doug