linux-kernel - Re: [PATCH 1/2] mmc: core: Improve marking broken HPI through devicetree

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Date:	Tue, 19 Apr 2016 21:20:18 +0200
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	Olliver Schinagl <oliver@...inagl.nl>
Cc:	Hans de Goede <hdegoede@...hat.com>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Chen-Yu Tsai <wens@...e.org>,
	Venu Byravarasu <vbyravarasu@...dia.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Michal Hocko <mhocko@...e.com>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Sudeep Holla <Sudeep.Holla@....com>,
	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
	Wolfram Sang <wsa+renesas@...g-engineering.com>,
	Wenkai Du <wenkai.du@...el.com>,
	Chaotian Jing <chaotian.jing@...iatek.com>,
	Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>,
	Jaehoon Chung <jh80.chung@...sung.com>,
	Michal Suchanek <hramrach@...il.com>,
	linux-mmc <linux-mmc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/2] mmc: core: Improve marking broken HPI through devicetree

[...]

> Well I think we still have a very small sample size, the sun4i, sun5i and
> sun7i boards (all using the same mmc controller afaik) have the broken-hpi
> set, the sun6i and sun8i seem to be working fine (different mmc
> controller?).
> I'm not so sure it is an eMMC specific problem though. The module we're
> using is a high-end micron part, industrial grade. Granted, it could be
> still broken there, but I find it less likely. Micron has an interessting
> technical document:
> "TN-52-05 e.EMMC Linux Enablement"
> talking specifically about HPI on eMMC.
> It also mentions HPI is a mmc/jedic 4.41 thing, afaik our controller is only
> 4.3 (which might not even matter according to Ulf if it is just a command).
>
> The datasheet of the chip I use, MTFC4GACAANA, also mentions explicitly that
> it supports HPI.
>
> Granted, it could still be broken, but I have doubts.

Perhaps the same eMMC is used without errors on other controllers?

>
>>
>> But given how rare eMMC-s are on sun4i/sun5i/sun7i I think the current
>> solution where we set a flag on the emmc dt node rather then on the
>> host node / in the host driver is fine.
>
> Yeah it is very limited, that is true, and I suppose I can live with that.
>>
>>
>> Taking your case into account too, that will bring us up to 2 cases
>> where we set the broken-hpi flag on the emmc node, which does not
>> really seem like a number to worry about.
>
> Actually, 4 :), there are 3 sun5i (tablets?) devices that suffer from this
> and my device now. The sun6i and sun8i devices are only 2 (the sinlinx
> devices in the current kernel) that a very quick grep (mmc-card ) showed.
> Grepping for non-removable yielded a bit more, like the chip sun5i-like
> device with a "non-removable" mmc, not sure what to make of that though.
>>
>>
>> TL;DR: Thanks for writing this patch set, but given recent developments
>> I believe that it is best to keep handling broken-hpi as we are doing
>> in current kernels and no changes are necessary.
>
> I would still recommend to add the capability and raise the flag for the
> sun[457]i devices though, as my gut thinks it's a problem with the sunxi IP
> there. But with the emmc-card level work around, it does solve/fix it, so
> what is the best way?

The best is clearly to make a proper debug investigation before we
decide to add a DT binding for the host.

I don't know on what level you are able to measure signals on the HW,
but if not, perhaps the newly TRACE support in the MMC core can help.

Kind regards
Uffe