linux-kernel - Re: [PATCH] ARM: rockchip: disable dapswjdp during suspend

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Message-ID: <CAD=FV=W6yw8TN7GpwU-fn5WAkNSc0MYSWgQbSuurKCdM+8d5Gw@mail.gmail.com>
Date:	Wed, 15 Apr 2015 15:38:12 -0700
From:	Doug Anderson <dianders@...omium.org>
To:	Chris Zhong <zyw@...k-chips.com>
Cc:	Heiko Stübner <heiko@...ech.de>,
	Dmitry Torokhov <dtor@...omium.org>,
	Sonny Rao <sonnyrao@...omium.org>,
	"open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
	Russell King <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ARM: rockchip: disable dapswjdp during suspend

Chris,

On Tue, Apr 14, 2015 at 10:57 PM, Chris Zhong <zyw@...k-chips.com> wrote:
> Reset dapswjdp is controlled by JTAG_TRSTN, if the iomux of this pin is
> not "jtag_trstn". the AP would think this pin is always high, so it can
> not reset before resume. When system resume, but the dapswjdp is not in
> a default state, it may Access some illegal address, it cause system
> crash during resume.
> Let's disable this jtag function by clear the dapdeviceen bit, it
> prohibit the dapswjdp to access memory and registers. This bit would
> be enable in MASKROM, so we need clear it in suspend everytime.
>
> Signed-off-by: Chris Zhong <zyw@...k-chips.com>
>
> ---
>
>  arch/arm/mach-rockchip/pm.c | 7 +++++++
>  arch/arm/mach-rockchip/pm.h | 4 ++++
>  2 files changed, 11 insertions(+)

I can't say that I understand 100% of the interactions here, but I
don't think anyone without full access to the MaskROM code would be
able to understand this fully.

...but this seems sane to me.  I guess disabling it here and then
enabling it in the MaskROM will effectively give it a good reset so
we're all good.

Reviewed-by: Doug Anderson <dianders@...omium.org>

I'll trust your testing on this, since you have actual machines that
reproduce the issue.

-Doug
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