linux-kernel - Re: [PATCH v1] sdhci: tegra: Add workaround for Broadcom WiFi

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Date:   Thu, 12 Dec 2019 16:07:24 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        linux-tegra <linux-tegra@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] sdhci: tegra: Add workaround for Broadcom WiFi

On Thu, 12 Dec 2019 at 15:23, Dmitry Osipenko <digetx@...il.com> wrote:
>
> 11.12.2019 19:29, Dmitry Osipenko пишет:
> > 11.12.2019 19:10, Ulf Hansson пишет:
> >> On Wed, 11 Dec 2019 at 16:46, Dmitry Osipenko <digetx@...il.com> wrote:
> >>>
> >>> Hello Ulf,
> >>>
> >>> 11.12.2019 11:11, Ulf Hansson пишет:
> >>>> On Tue, 10 Dec 2019 at 02:40, Dmitry Osipenko <digetx@...il.com> wrote:
> >>>>>
> >>>>> All Tegra20 boards that have embedded Broadcom WiFi SDIO chip are affected
> >>>>> by a problem where WiFi chip reports CCCR v1.10, while it should v1.20.
> >>>>> In a result high-speed mode isn't enabled for the WiFi card and this
> >>>>> results in a malfunctioning SDIO communication.
> >>>>
> >>>> Does that also mean SDIO_SPEED_SHS bit is set when reading SDIO_CCCR_SPEED?
> >>>
> >>> Yes, the SDIO_SPEED_SHS bit is set.
> >>>
> >>>>>  brcmfmac: brcmf_sdio_readframes: read 304 bytes from channel 1 failed: -84
> >>>>>  brcmfmac: brcmf_sdio_rxfail: abort command, terminate frame, send NAK
> >>>>>
> >>>>> Downstream kernels are overriding card's CCCR info in SDHCI driver to fix
> >>>>> the problem, let's do the same in upstream.
> >>>>>
> >>>>> The change is inspired by omap_hsmmc_init_card() of OMAP's HSMMC driver,
> >>>>> which overrides card's info for the TI wl1251 WiFi.
> >>>>
> >>>> This is a temporary solution and should be replaced by doing the DT
> >>>> parsing during
> >>>>
> >>>> So, yes, let's see if we can use a card quirk instead. That's the first option.
> >>>>
> >>>> A second option is simply to parse the DT subnode for a new DT
> >>>> property during mmc_sdio_init_card(). Along the lines of what we do
> >>>> for the broken-hpi DT binding for eMMC.
> >>>
> >>> Let's try the first option. My understanding is that the problem affects
> >>> only the specific model of the WiFi chip and it's not a board-specific
> >>> problem. I'll add Broadcom driver people to CC for the next version of
> >>> the patch, maybe they'll have something to say.
> >>
> >> Okay, sounds reasonable. By looking at your latest attempt for a fix,
> >> I have two minor nitpicks, otherwise it looks good.
> >>
> >> The nitpicks:
> >> I suggest to rename MMC_QUIRK_HIGH_SPEED_CARD to MMC_QUIRK_HIGH_SPEED
> >> and mmc_card_need_high_speed_toggle() to mmc_card_quirk_hs().
> >
> > I'll take it into account, thanks.
>
> Looks like I managed to figure out what's really going on:
>
>   1. The BCM4329 doc clearly states that High Speed is supported, see
> page 49 (Section 11: WLAN Interfaces, SDIO v1.2)
>
> https://www.cypress.com/file/298626/download
>
>   2. I googled for performance results of the BCM4329 SDIO WiFi and came
> to a conclusion that ~40 Mbit/s is a realistic maximum of the WiFi-data
> throughput for NVIDIA Tegra20 boards due to antenna configuration
> limitations and whatever.

Okay.

>
>   3. The Tegra's SDHCI clock is pre-configured to 48MHz at the time of
> kernel's boot-up.
>
>   4. IIUC, the maximum clock rate for the legacy SD signaling mode is
> ~25MHz and that is more than enough for a 4-lane SDIO data-bus that
> allows up to 100 Mbit/s for the WiFi which is capped to 40 Mbit/s anyways.

Yes, I see.

>
>   5. Apparently MMC core doesn't limit the clock rate for the Normal
> Speed cards.

It should, else it's a bug (I would be really surprised if that's the
case, but who knows).

>
>
> So, I added "max-frequency = <25000000>;" to the SDHCI node of the
> board's device-tree and ta-da! WiFi works absolutely fine without the
> quirk! Thus the SDIO card quirk isn't really needed and I'm dropping it
> for now.
>
> Ulf, do you know if it's a bug or a feature of the MMC core that it
> doesn't limit clock rate for the Normal Speed cards?

It should limit the speed, else it's a bug. Can you perhaps check what
the requested clock rate is via some debug prints in the host ops
->set_ios()? And also what the real rate becomes after dividers.

If it's not a bug in the core, I suspect that there may be generic
problem dealing with initialization frequencies for sdhci-tegra.

For example, mmc_rescan_try_freq() tries to initialize the SDIO card
at 400KHz, then 300, then 200 then 100 (in that order, and note
*KHz*). When a frequency is successful, initialization continues and
later on the clock rate should be increased to 25MHz, for legacy speed
mode.

Kind regards
Uffe