Re: [PATCH v4 5/5] brcmfmac: sdio: Don't tune while the card is off

[Arend Van Spriel]

On 6/14/2019 1:41 AM, Douglas Anderson wrote:
> When Broadcom SDIO cards are idled they go to sleep and a whole
> separate subsystem takes over their SDIO communication.  This is the
> Always-On-Subsystem (AOS) and it can't handle tuning requests.
>
> Specifically, as tested on rk3288-veyron-minnie (which reports having
> BCM4354/1 in dmesg), if I force a retune in brcmf_sdio_kso_control()
> when "on = 1" (aka we're transition from sleep to wake) by whacking:
>    bus->sdiodev->func1->card->host->need_retune = 1
> ...then I can often see tuning fail.  In this case dw_mmc reports "All
> phases bad!").  Note that I don't get 100% failure, presumably because
> sometimes the card itself has already transitioned away from the AOS
> itself by the time we try to wake it up.  If I force retuning when "on
> = 0" (AKA force retuning right before sending the command to go to
> sleep) then retuning is always OK.
>
> NOTE: we need _both_ this patch and the patch to avoid triggering
> tuning due to CRC errors in the sleep/wake transition, AKA ("brcmfmac:
> sdio: Disable auto-tuning around commands expected to fail").  Though
> both patches handle issues with Broadcom's AOS, the problems are
> distinct:
> 1. We want to defer (but not ignore) asynchronous (like
>     timer-requested) tuning requests till the card is awake.  However,
>     we want to ignore CRC errors during the transition, we don't want
>     to queue deferred tuning request.
> 2. You could imagine that the AOS could implement retuning but we
>     could still get errors while transitioning in and out of the AOS.
>     Similarly you could imagine a seamless transition into and out of
>     the AOS (with no CRC errors) even if the AOS couldn't handle
>     tuning.
>
> ALSO NOTE: presumably there is never a desperate need to retune in
> order to wake up the card, since doing so is impossible.  Luckily the
> only way the card can get into sleep state is if we had a good enough
> tuning to send it a sleep command, so presumably that "good enough"
> tuning is enough to wake us up, at least with a few retries.

The term "sleep command" is a bit confusing. There actually is a CMD14 
defined in the eSD spec, but that is not what we are using (unless we 
program the chip to do so) here. It is simply a specific register access 
using CMD52.

Apart from that....

Reviewed-by: Arend van Spriel <arend.vanspriel@xxxxxxxxxxxx>
> Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>

I think the stable version is mostly determined by change in MMC/SDIO so 
4.18 as mentioned Adrian seems most sensible. bcm4354 support was 
introduced in 3.14 and there were some earlier devices (4335) using same 
sleep mechanism.

Regards,
Arend