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

From: Dmitry Osipenko
Date: Thu Dec 12 2019 - 09:24:00 EST

11.12.2019 19:29, Dmitry Osipenko ÐÐÑÐÑ:
> 11.12.2019 19:10, Ulf Hansson ÐÐÑÐÑ:
>> On Wed, 11 Dec 2019 at 16:46, Dmitry Osipenko <digetx@xxxxxxxxx> wrote:
>>> Hello Ulf,
>>> 11.12.2019 11:11, Ulf Hansson ÐÐÑÐÑ:
>>>> On Tue, 10 Dec 2019 at 02:40, Dmitry Osipenko <digetx@xxxxxxxxx> 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:
>> 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)

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.

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.

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

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?