linux-kernel - Re: [PATCH 1/2] mmc: core: Support all MMC capabilities when booting from Device Tree

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Message-ID: <1B3089FB-EDBE-4145-83A6-1DFA4B0A2FDF@nvidia.com>
Date:	Wed, 17 Oct 2012 21:56:32 +0200
From:	Philip Rakity <prakity@...dia.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	Lee Jones <lee.jones@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linus.walleij@...ricsson.com" <linus.walleij@...ricsson.com>,
	Chris Ball <cjb@...top.org>,
	Russell King <linux@....linux.org.uk>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	Ulf Hansson <ulf.hansson@...ricsson.com>
Subject: Re: [PATCH 1/2] mmc: core: Support all MMC capabilities when
 booting from Device Tree


On 17 Oct 2012, at 14:38, Arnd Bergmann <arnd@...db.de> wrote:

> On Monday 15 October 2012, Lee Jones wrote:
>>> and so on. What are you actually missing in the properties that
>>> are already there?
>> 
>> MMC_CAP_ERASE
> 
> This one seems to be set unconditionally on some controllers but
> not on others. Why would it need to be configurable?
> 
>> MMC_CAP_UHS_SDR12
>> MMC_CAP_UHS_SDR25
>> MMC_CAP_UHS_DDR50
> 
> Could this be derived from max-frequency?

The problem is the controller may signal it supports DDR but the host cannot.  For example no voltage at correct level.
Same issue with 8 bit support.  Controller could say supports it but board has only 4 "wires"
> 
>> MMC_CAP_1_8V_DDR
> 
> Right, I suppose we need this. Should we have a minimum and maximum
> voltage added to the common properties for this?
> 
>> MMC_CAP2_DETECT_ON_ERR
>> MMC_CAP2_NO_SLEEP_CMD
> 
> I don't see these ones being set anywhere, but they were both
> added by Ulf. Maybe he can comment on if or why they are needed
> in devicetree, rather than being set by the driver unconditionally
> or for specific versions of the host controller.
> 
> 	Arnd
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