linux-kernel - Re: [PATCH v2 06/12] mmc: pwrseq: add support for power-on sequencing through DT

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Message-ID: <568FAA07.1010509@osg.samsung.com>
Date:	Fri, 8 Jan 2016 09:22:31 -0300
From:	Javier Martinez Canillas <javier@....samsung.com>
To:	Caesar Wang <wxt@...k-chips.com>, Heiko Stuebner <heiko@...ech.de>,
	Ulf Hansson <ulf.hansson@...aro.org>
Cc:	linux-rockchip@...ts.infradead.org, leecam@...gle.com,
	leozwang@...gle.com, keescook@...gle.com,
	Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
	linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
	Alexandre Courbot <acourbot@...dia.com>,
	NeilBrown <neil@...wn.name>
Subject: Re: [PATCH v2 06/12] mmc: pwrseq: add support for power-on sequencing
 through DT

Hello Caesar,

On 01/07/2016 05:25 AM, Caesar Wang wrote:
> This patch enables support for power-on sequencing of SDIO
> peripherals through DT.
>

I think the subject line and this first paragraph are misleading since
the simple power sequence provider already supports power-on sequencing.

This patch does not add or enable support but extends the current support
to also enable a regulator as a part of the SDIO chip power on sequencing.

> In general, it's quite common that wifi modules and other similar
> peripherals have several signals in addition to the SDIO interface that
> needs wiggling before the module will power on.
> 
> For example:
> we need enable wifi module power to via the WL_REG_ON
> pin, we need enable it as the regulator if this pin is connected to
> the gpio of cpu.
>

This part confuses me, so does your chip have an actual regulator that
needs to be enabled or is just a fake regulator whose gpio property is
used not to enable the regulator but to toggle the WL_REG_ON pin of
the WiFi chip?

> Maybe, someone will say that can pull up/down from dts.
> Unfortunately some SoCs can't support pinctrl pull up/down in
> internal.
>

Can you please elaborate on this? AFAIU this limitation is the reason
why you went with the regulator approach so I think it deserve a more
deep explanation.

> Anyway, we can add this patch to supprt the power-on sequencing for

s/supprt/support

> sdio.
> 
> Signed-off-by: Caesar Wang <wxt@...k-chips.com>
> 

Best regards,
-- 
Javier Martinez Canillas
Open Source Group
Samsung Research America