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

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Date:   Thu, 3 Nov 2016 19:00:17 +0530
From:   "Sricharan" <sricharan@...eaurora.org>
To:     "'Stephen Boyd'" <sboyd@...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

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.
>
 Ok, so the video ip core, has a hw control signal/bit.
 I checked this by dumping this out that,  the moment the
gdsc is put to hw control, the video ip's hw control bit also
gets asserted/set. so this means that video ip's bit get
aligned with the gdsc setting.  so this should avoid the
glitches, right ?

Regards,
 Sricharan