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

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Date:   Tue, 20 Nov 2018 16:09:32 +0530
From:   Faiz Abbas <faiz_abbas@...com>
To:     Wolfram Sang <wsa@...-dreams.de>,
        Ulf Hansson <ulf.hansson@...aro.org>
CC:     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

Hi,

On 20/11/18 3:53 PM, Wolfram Sang wrote:
> 
>>>> 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"?

At least for me, the failure happens only on some units but is
consistent for a given unit.

> 
> 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.
> 

The QUIRK needs to be card specific. The software should automatically
detect the card (from the CID) and apply the quirk. Please see patch in
my original reply.

Thanks,
Faiz