linux-kernel - Re: [PATCH v2 3/3] brcmfmac: sdio: Disable auto-tuning around commands expected to fail

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Date:   Fri, 07 Jun 2019 07:12:42 +0200
From:   Arend Van Spriel <arend.vanspriel@...adcom.com>
To:     Doug Anderson <dianders@...omium.org>,
        Adrian Hunter <adrian.hunter@...el.com>
CC:     Ulf Hansson <ulf.hansson@...aro.org>,
        Kalle Valo <kvalo@...eaurora.org>,
        <brcm80211-dev-list.pdl@...adcom.com>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        Double Lo <double.lo@...ress.com>,
        Brian Norris <briannorris@...omium.org>,
        "linux-wireless" <linux-wireless@...r.kernel.org>,
        Naveen Gupta <naveen.gupta@...ress.com>,
        Madhan Mohan R <madhanmohan.r@...ress.com>,
        Matthias Kaehlcke <mka@...omium.org>,
        Wright Feng <wright.feng@...ress.com>,
        "Chi-Hsien Lin" <chi-hsien.lin@...ress.com>,
        netdev <netdev@...r.kernel.org>,
        "brcm80211-dev-list" <brcm80211-dev-list@...ress.com>,
        "David S. Miller" <davem@...emloft.net>,
        Franky Lin <franky.lin@...adcom.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Hante Meuleman <hante.meuleman@...adcom.com>,
        YueHaibing <yuehaibing@...wei.com>,
        Michael Trimarchi <michael@...rulasolutions.com>
Subject: Re: [PATCH v2 3/3] brcmfmac: sdio: Disable auto-tuning around commands expected to fail

On June 6, 2019 11:37:22 PM Doug Anderson <dianders@...omium.org> wrote:
>
> In the case of dw_mmc, which I'm most familiar with, we don't have any
> sort of automated or timed-based retuning.  ...so we'll only re-tune
> when we see the CRC error.  If I'm understanding things correctly then
> that for dw_mmc my solution and yours behave the same.  That means the
> difference is how we deal with other retuning requests, either ones
> that come about because of an interrupt that the host controller
> provided or because of a timer.  Did I get that right?

Right.

> ...and I guess the reason we have to deal specially with these cases
> is because any time that SDIO card is "sleeping" we don't want to
> retune because it won't work.  Right?  NOTE: the solution that would
> come to my mind first to solve this would be to hold the retuning for
> the whole time that the card was sleeping and then release it once the
> card was awake again.  ...but I guess we don't truly need to do that
> because tuning only happens as a side effect of sending a command to
> the card and the only command we send to the card is the "wake up"
> command.  That's why your solution to hold tuning while sending the
> "wake up" command works, right?

Yup.

> ---
>
> OK, so assuming all the above is correct, I feel like we're actually
> solving two problems and in fact I believe we actually need both our
> approaches to solve everything correctly.  With just your patch in
> place there's a problem because we will clobber any external retuning
> requests that happened while we were waking up the card.  AKA, imagine
> this:
>
> A) brcmf_sdio_kso_control(on=True) gets called; need_retune starts as 0
>
> B) We call sdio_retune_hold_now()
>
> C) A retuning timer goes off or the SD Host controller tells us to retune
>
> D) We get to the end of brcmf_sdio_kso_control() and clear the "retune
> needed" since need_retune was 0 at the start.
>
> ...so we dropped the retuning request from C), right?
>
>
> What we truly need is:
>
> 1. CRC errors shouldn't trigger a retuning request when we're in
> brcmf_sdio_kso_control()
>
> 2. A separate patch that holds any retuning requests while the SDIO
> card is off.  This patch _shouldn't_ do any clearing of retuning
> requests, just defer them.
>
>
> Does that make sense to you?  If so, I can try to code it up...

FWIW it does make sense to me. However, I am still not sure if our sdio 
hardware supports retuning. Have to track down an asic designer who can 
tell or dive into vhdl myself.

So I want to disable device sleep and trigger retuning through debugfs or 
some other hack.

Regards,
Arend