linux-kernel - Re: [PATCH 1/3] clk: qcom: gdsc: Add support for gdscs with HW control

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Date:   Wed, 2 Nov 2016 10:59:44 -0700
From:   'Stephen Boyd' <sboyd@...eaurora.org>
To:     Sricharan <sricharan@...eaurora.org>
Cc:     mturquette@...libre.com, linux-clk@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        rnayak@...eaurora.org, stanimir.varbanov@...aro.org
Subject: Re: [PATCH 1/3] clk: qcom: gdsc: Add support for gdscs with HW
 control

On 11/02, Sricharan wrote:
> Hi Stephen,
> 
> >On 10/24, Sricharan R wrote:
> >> @@ -164,6 +171,10 @@ static int gdsc_enable(struct generic_pm_domain *domain)
> >>  	 */
> >>  	udelay(1);
> >>
> >> +	/* Turn on HW trigger mode if supported */
> >> +	if (sc->flags & HW_CTRL)
> >> +		gdsc_hwctrl(sc, true);
> >> +
> >
> >It sounds like this will cause glitches if the hardware isn't
> >asserting their hw control bit by default? This has me concerned
> >that we can't just throw the hw control enable part into here,
> >because that bit doesn't live in the clock controller, instead it
> >lives in the hw block that is powered by the power domain?
> >
> >Or does the power on reset value of that hw control signal
> >asserted? If that's true then we should be ok to force it into hw
> >control mode by default.
> >
> 
> The hw control bit is set by default. Instead its turned 'off'
> with the reset value. So it has to not 
> be turned 'on' at some point
> to put the gdsc in hw control if required. This bit is part of the
> gdscr register. So i did not quite understand the reason for the
> glitch here ?

I mean the reset value of the hw control signal inside the device
that is inside the GDSC power domain. For example, the hw control
bit inside the video core.

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