From mboxrd@z Thu Jan  1 00:00:00 1970
From: mturquette@linaro.org (Mike Turquette)
Date: Tue, 27 Nov 2012 09:29:00 -0800
Subject: [PATCH v3 02/11] clk: davinci - add PSC clock driver
In-Reply-To: <50B4D6B1.3000903@ti.com>
References: <1351181518-11882-1-git-send-email-m-karicheri2@ti.com>
 <1351181518-11882-3-git-send-email-m-karicheri2@ti.com>
 <50950908.1060302@ti.com> <5097D6FC.7040202@ti.com>
 <20121110022254.18014.31873@nucleus> <50B4D6B1.3000903@ti.com>
Message-ID: <20121127172900.21126.89528@nucleus>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

Quoting Sekhar Nori (2012-11-27 07:05:21)
> Hi Mike,
> 
> On 11/10/2012 7:52 AM, Mike Turquette wrote:
> > Quoting Murali Karicheri (2012-11-05 07:10:52)
> >> On 11/03/2012 08:07 AM, Sekhar Nori wrote:
> >>> On 10/25/2012 9:41 PM, Murali Karicheri wrote:
> >>>> This is the driver for the Power Sleep Controller (PSC) hardware
> >>>> found on DM SoCs as well Keystone SoCs (c6x). This driver borrowed
> >>>> code from arch/arm/mach-davinci/psc.c and implemented the driver
> >>>> as per common clock provider API. The PSC module is responsible for
> >>>> enabling/disabling the Power Domain and Clock domain for different IPs
> >>>> present in the SoC. The driver is configured through the clock data
> >>>> passed to the driver through struct clk_psc_data.
> >>>>
> >>>> Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
> >>>> ---
> >>>> +/**
> >>>> + * struct clk_psc - DaVinci PSC clock driver data
> >>>> + *
> >>>> + * @hw: clk_hw for the psc
> >>>> + * @psc_data: Driver specific data
> >>>> + */
> >>>> +struct clk_psc {
> >>>> +    struct clk_hw hw;
> >>>> +    struct clk_psc_data *psc_data;
> >>>> +    spinlock_t *lock;
> >>> Unused member? I don't see this being used.
> >>
> >> OK. Will remove.
> > 
> > Those locks are only used for the case where a register might contain
> > bits for several clocks.  Thus RMW operations are protected.  On OMAP
> > this isn't necessary due to a very generous register layout (typically
> > one 32-bit reg per module) controlling clocks.  Seems tha tmaybe this is
> > not needed for PSC module either?
> 
> Sorry about the late reply. The above is not totally true for PSC. There
> are some registers (like PTCMD) which are common for all clocks.
> 
> There is an enable_lock used in drivers/clk/clk.c which serializes all
> enable/disable calls across the clock tree. Since that is done, further
> locking at clk-psc level is not really needed, no?
> 

I haven't finished looking through the PSC design document yet, but my
answer to your question is this:

If a register is only used for clk_enable/disable calls (not touched by
anything held under the prepare_lock mutex) and if that register isn't
used anywhere else in the code (outside of the clk framework) then yes,
the enable_lock spinlock is enough for you.

Also have you looked into regmap?  Since you are defining your own clock
type that might be something nice for you.

Regards,
Mike

> Thanks,
> Sekhar