linux-kernel - Re: [PATCH] mmc: core: Remove timeout when enabling cache

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Date:   Tue, 20 Nov 2018 11:23:01 +0100
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Faiz Abbas <faiz_abbas@...com>,
        Sjoerd Simons <sjoerd.simons@...labora.co.uk>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        kernel@...labora.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Hongjie Fang <hongjiefang@...micro.com>,
        Bastian Stender <bst@...gutronix.de>,
        Kyle Roeschley <kyle.roeschley@...com>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Shawn Lin <shawn.lin@...k-chips.com>,
        Harish Jenny K N <harish_kandiga@...tor.com>,
        Simon Horman <horms+renesas@...ge.net.au>
Subject: Re: [PATCH] mmc: core: Remove timeout when enabling cache


> >> That also happens to be one of the cards we deploy; However i did
> >> wonder about adding a quirk but decided against it as it was not clear
> >> to me from the specification that CACHE ON really is meant to complete
> >> within GENERIC_CMD6_TIMEOUT. That and i fret about ending up in hit-a-
> >> mole games as the failure is really quite tedious (boot failure).
> >
> > I agree that we should use the more defensive variant as a default. I
> > mean there should be no performance regression since most cards will
> > respond just faster, or? The only downside I could see is that we might
> > miss a real timeout with no bounds set and might get stuck?
> 
> Well, you have a point, but still it's kind of nice to know which
> cards are behaving well and which ones that doesn't. Hence I think I
> prefer to stick using a quirk, unless you have a strong opinion.

No strong opinion. Especially not if you say it is in the spec (although
"must be sufficient" would be better than "should be" ;)). Also, I
assume this failure is reproducible and should turn up during
development? Compared to "happens once in a while randomly"?

Yet, if we add a quirk for that, then we should probably mention it in
an error message when we hit -ETIMEDOUT for cache on ("does your card
need this quirk?")? It can be pretty time consuming to track this down
otherwise, I'd think.


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