linux-kernel - Re: [PATCH v3 2/2] mmc: dw_mmc: add resets support to dw

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Date:	Mon, 04 Apr 2016 12:54:03 +0900
From:	Jaehoon Chung <jh80.chung@...sung.com>
To:	Heiko Stuebner <heiko@...ech.de>
Cc:	Guodong Xu <guodong.xu@...aro.org>, shawn.lin@...k-chips.com,
	"robh+dt@...nel.org" <robh+dt@...nel.org>, pawel.moll@....com,
	mark.rutland@....com, ijc+devicetree@...lion.org.uk,
	galak@...eaurora.org, ulf.hansson@...aro.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	Xinwei Kong <kong.kongxinwei@...ilicon.com>,
	Zhangfei Gao <zhangfei.gao@...aro.org>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>
Subject: Re: [PATCH v3 2/2] mmc: dw_mmc: add resets support to dw_mmc

On 04/02/2016 03:42 AM, Heiko Stuebner wrote:
> Am Mittwoch, 30. März 2016, 20:40:31 schrieb Jaehoon Chung:
>> modified Rob's mail address.
>>
>> On 03/30/2016 04:24 PM, Guodong Xu wrote:
>>> mmc registers may in abnormal state if mmc is used in bootloader,
>>> eg. to support booting from eMMC. So we need reset mmc registers
>>> when kernel boots up, instead of assuming mmc is in clean state.
>>
>> Do you mean mmc(card side) register or dwmmc host controller's register on
>> host side?
>>
>> According to dwmmc controller TMR, there are two reset signals. One is
>> reset_n, other is rst_n. It seems this patch is relevant to reset_n(For
>> host). (rst_n is hardware reset for card.)
>>
>> So could you clarify better? Then it's helpful to me for understanding..
> 
> I think that actually means a reset of controller IP block logic, outside 
> the control of the dw_mmc block itself.
> 
> On Rockchip SoCs this gets triggered from the CRU (clock and reset unit), so 
> I guess if I'm reading the manual correctly, should be the reset_n signal of 
> the ip block.
> 
> rst_n on the other hand gets triggered through a dw_mmc register setting and 
> is already handled by the dw_mmc driver.

Right, this patch is for reset_n signal. I didn't have seen the SoC that reset_n is designed.
(Or i didn't realize...)
If Rockchip is used from CRU (clock and reset unit), then i think that it makes sense.

Thanks for explanation. 

Best Regards,
Jaehoon Chung

> 
> 
> Heiko
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