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

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Date:	Wed, 30 Mar 2016 09:18:46 +0800
From:	zhangfei <zhangfei.gao@...aro.org>
To:	Shawn Lin <shawn.lin@...k-chips.com>,
	Guodong Xu <guodong.xu@...aro.org>
CC:	robh+dt@...nel.org,
	Paweł Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	ijc+devicetree@...lion.org.uk, Kumar Gala <galak@...eaurora.org>,
	jh80.chung@...sung.com, Ulf Hansson <ulf.hansson@...aro.org>,
	devicetree@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-mmc@...r.kernel.org,
	Xinwei Kong <kong.kongxinwei@...ilicon.com>
Subject: Re: [PATCH 2/2] mmc: dw_mmc: add resets support to dw_mmc



On 03/30/2016 08:46 AM, Shawn Lin wrote:
> 在 2016/3/29 16:23, zhangfei 写道:

>>> More to think, Is it ok to match the behaviour of bootloader stage?
>>> My bootloader doesn't assert the reset pin of dw_mmc, so it seams if
>>> I want to fix you issue on kernel stage, I need a new round of
>>> assert->delay->deassert.
>>
>> The process like delay (if required) should be abstracted in reset
>> driver.
>> reset framework just export reset_control_assert/reset_control_deassert
>> API.
>> Unfortunately not find clear description in Documentation/.
>> Suppose deassert is like start, while assert is like stop.
>>
>
> yes, no docs except dt-bindings..... So seems the usage of these two
> APIs depends on the implementation of reset controller driver
>
>> drivers/reset/core.c
>> reset_control_deassert - deasserts the reset line
>> reset_control_assert - asserts the reset line
>>
>> More example:
>> drivers/mmc/host/sdhci-st.c
>> drivers/mmc/host/sunxi-mmc.c
>> drivers/usb/host/ohci-platform.c
>> drivers/i2c/busses/i2c-mv64xxx.c
>
> But I'm afraid I have to nack here....
>
> Looking at these files:
> drivers/dma/stm32-dma.c
> drivers/net/ethernet/mediatek/mtk_eth_soc.c
> drivers/devfreq/tegra-devfreq.c
> drivers/crypto/rockchip/rk3288_crypto.c
> drivers/thermal/rockchip_thermal.c
> drivers/thermal/tegra_soctherm.c
> drivers/i2c/busses/i2c-tegra.c
> ....
>
> they just do the way like: assert->[delay](maybe abstracted)->deassert
> I think these drivers are vendor specific, so they can do
> the reset operations in consistent with the implementation of
> their platforms' reset controller drivers.

Yes, have checked drivers/i2c/busses/i2c-tegra.c
         reset_control_assert(i2c_dev->rst);
         udelay(2);
         reset_control_deassert(i2c_dev->rst);

This usage looks strange, reset does not mean gpio reset, it maybe 
register accessing.
I think all these three operation should be abstracted to deassert 
function, while cover the details for sharing.

However, not doc describing the assert/deassert behavior so causing 
confusion.

>
> But, dw_mmc is shared by many Socs. So It's not good to do it in
> dw_mci_probe, otherwise you force my reset controller driver to be
> implemented in the same way as yours..... Right?
>
> How about move it to your drv_data->init callback?
Yes, we can.
But firstly we should consider put in common file for sharing, otherwise 
there maybe many assert/deassert in dw_mmc-xx.c.

Guodong may send another version and wait for Jaehoon's decision.

Thanks