RE: [PATCH 9/9] clk: imx: add imx7ulp clk driver

[A.s. Dong]

> -----Original Message-----
> From: Stephen Boyd [mailto:sboyd@xxxxxxxxxxxxxx]
> Sent: Saturday, July 01, 2017 8:35 AM
> To: A.s. Dong
> Cc: Dong Aisheng; linux-clk@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; mturquette@xxxxxxxxxxxx;
> shawnguo@xxxxxxxxxx; Anson Huang; Jacky Bai
> Subject: Re: [PATCH 9/9] clk: imx: add imx7ulp clk driver
> 
> On 06/21, A.s. Dong wrote:
> > > -----Original Message-----
> > > From: Stephen Boyd [mailto:sboyd@xxxxxxxxxxxxxx]
> > > Sent: Wednesday, June 21, 2017 4:42 AM
> > > To: Dong Aisheng
> > > Cc: A.s. Dong; linux-clk@xxxxxxxxxxxxxxx;
> > > linux-kernel@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx;
> > > mturquette@xxxxxxxxxxxx; shawnguo@xxxxxxxxxx; Anson Huang; Jacky Bai
> > > Subject: Re: [PATCH 9/9] clk: imx: add imx7ulp clk driver
> > >
> > > On 06/20, Dong Aisheng wrote:
> > > > On Mon, Jun 19, 2017 at 07:01:19PM -0700, Stephen Boyd wrote:
> > > > >
> > > > > Any reason why it can't be a platform driver? If not, please add
> > > > > some comment explaining why.
> > > > >
> > > >
> > > > Timer is using it at early stage. GIC seems not although standard
> > > > binding claim possible clock requirement.
> > > > Others still not sure.
> > > >
> > > > What your suggestion?
> > > > Convert timer to platform driver and make clock as platform driver
> > > > as
> > > well?
> > > >
> > >
> > > The timer can't be a platform driver because it would be too late.
> > > The clock driver could register whatever clks are required for the
> > > timer/GIC in a CLK_OF_DECLARE_DRIVER hook, and then leave the rest
> > > to a platform driver. This way we get some of the device driver
> framework in this code.
> > >
> >
> > Okay, I could try it. Thanks.
> >
> > One thing is that TPM clock has a lot parents and parents having
> > parents, as well as PIT timer. So I may need enable more than half
> > clocks in CLK_OF_DECLARE_DRIVER hook.
> 
> That's fine.
> 
> >
> > BTW, What's benefit to convert into two parts of probe?
> > I'm not quite if I already get it all, can you help clarify it?
> >
> 
> The benefit is that we still get a platform driver and we can associate a
> device pointer with the clock controller eventually.
> Here's a reply I sent yesterday on the same topic:
> 
> Reasons (in no particular order):
> 
>   1. We get a dev pointer to use with clk_hw_register()
> 
>   2. We can handle probe defer if some resource is not available
> 
>   3. Using device model gets us a hook into power management frameworks
>      like runtime PM and system PM for things like suspend and hibernate
> 
>   4. It encourages a single DT node clk controller style binding
>      instead of a single node per clk style binding
> 
>   5. We can use non-DT specific functions like devm_ioremap_resource() to
> map
>      registers and acquire other resources, leading to more portable and
>      generic code
> 
>   6. We may be able to make the device driver a module, which will
>      make distros happy if we don't have to compile in all
>      these clk drivers to the resulting vmlinux (this one doesn't
>      apply here)
> 

Very clear.
Thanks for the great explanation.

Regards
Dong Aisheng

> --
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a
> Linux Foundation Collaborative Project