[PATCH v3 1/1] misc: sram: add dev_pm_ops to support module power gate

[Shenwei Wang]

> -----Original Message-----
> From: Sudeep Holla [mailto:sudeep.holla at arm.com]
> Sent: 2015年8月25日 8:03
> To: Wang Shenwei-B38339
> Cc: gregkh at linuxfoundation.org; arnd at arndb.de; Sudeep Holla; Huang
> Yongcai-B20788; linux-arm-kernel at lists.infradead.org
> Subject: Re: [PATCH v3 1/1] misc: sram: add dev_pm_ops to support module
> power gate
> 
> 
> 
> On 30/07/15 17:11, Shenwei Wang wrote:
> > When system goes into low power states like SUSPEND_MEM and
> > HIBERNATION, the hardware IP block may be powered off to reduce the
> > power consumption. This power down will lost all the data inside the
> > ram. This patch added the dev_pm_ops and implemented two callbacks:
> > suspend_noirq and resume_noirq, which will save the data in the
> > on-chip-ram right before power down and restore it after system
> > resumes.
> >
> 
> Who uses this SRAM ? Can't they be released before suspending ?
> This might not be feasible and time consuming as the size of SRAM increases.

On Freescale i.MX7D, we are using this kind of SRAM. As I implemented this as an 
optional feature, a user can balance between the suspend/resume time and the power
consumption.

> Also I just check the entire tree for the users of gen_pool, I found it's used for
> video/audio and crypto which needs to on-demand basis.
> Apart from that it's mainly used for low power modes in which case, SRAM needs
> to be powered on. So can you provide more details on your use-case.

On latest Freescale i.MX7D, it has two SRAMs in side. One is for low power mode which will be powered
on in suspend state. The other one is for other peripherals which can be powered off on demand.

Thanks,
Shenwei 

> > A new property string named "can-power-gate" is added to the
> > devicetree bindings too.
> >
> > Signed-off-by: Shenwei Wang <shenwei.wang at freescale.com>
> > Signed-off-by: Anson Huang <b20788 at freescale.com>
> > ---
> > Change log:
> >
> > PATCH v3
> > 	Removed the unnecessary clk_enable/clk_disable.
> >
> > PATCH v2
> > 	Use vmalloc to allocate the SRAM backup memory.
> > 	Code clean up.
> >
> >   Documentation/devicetree/bindings/misc/sram.txt |  2 ++
> >   drivers/misc/sram.c                             | 42
> +++++++++++++++++++++++++
> >   2 files changed, 44 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/misc/sram.txt
> > b/Documentation/devicetree/bindings/misc/sram.txt
> > index 36cbe5a..1170086 100644
> > --- a/Documentation/devicetree/bindings/misc/sram.txt
> > +++ b/Documentation/devicetree/bindings/misc/sram.txt
> > @@ -33,6 +33,8 @@ Optional properties in the area nodes:
> >
> >   - compatible : standard definition, should contain a vendor specific string
> >                  in the form <vendor>,[<device>-]<usage>
> > +- can-power-gate: a property to tell the driver that the sram can support
> > +		power gate
> >
> 
> Please cc device-tree list for such generic bindings.
> 
> Regards,
> Sudeep