RE: [PATCH 2/2] clk: imx: imx7d: remove clks_init_on array

[Anson Huang]

Hi, Stephen

Anson Huang
Best Regards!


> -----Original Message-----
> From: Stephen Boyd <sboyd@xxxxxxxxxx>
> Sent: Tuesday, October 16, 2018 12:46 AM
> To: kernel@xxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx;
> linux-clk@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> mturquette@xxxxxxxxxxxx; s.hauer@xxxxxxxxxxxxxx; shawnguo@xxxxxxxxxx;
> Anson Huang <anson.huang@xxxxxxx>; Fabio Estevam
> <fabio.estevam@xxxxxxx>; Jerome Forissier <jerome.forissier@xxxxxxxxxx>;
> Peng Fan <peng.fan@xxxxxxx>; Rob Herring <robh@xxxxxxxxxx>
> Cc: dl-linux-imx <linux-imx@xxxxxxx>
> Subject: RE: [PATCH 2/2] clk: imx: imx7d: remove clks_init_on array
> 
> Quoting Anson Huang (2018-10-15 02:33:35)
> > > > > >
> > > > >
> > > > > Why can't we add clks to the op-tee node in DT's /firmware container?
> > > > > Then any clks in there can be turned on forever and left enabled
> > > > > by the linux driver?
> > > >
> > > > I did NOT run op-tee with Linux-next kernel before, can you advise more?
> > >
> > > Neither have I, so I can't advise more.
> > >
> > > > And I think if op-tee has such requirement, can we have another
> > > > patch to cover it?
> > >
> > > Yes.
> > >
> > >
> > > > I believe all other i.MX platforms also have same requirements if
> > > > considering op-tee support, so I think it should be another topic,
> > > > what do you
> > > think?
> > > >
> > >
> > > I'm going to drop these patches from my review queue. Please resend
> > > them and please include the op-tee patches too.
> >
> >
> > I do NOT know how to include the op-tee patch to meet special
> > requirement, should the op-tee related patch be added later when someone
> actually add the op-tee support for i.MX7?
> > It should NOT block this patch set, do you think we can add this patch set
> first?
> >
> 
> Please resend the two patches. In the commit text for the second patch,
> describe the plan to remove CLK_IS_CRITICAL from these clks by adding an
> OP-TEE device/driver to the kernel to keep these clks enabled. My
> understanding is that there isn't an OP-TEE driver right now, but these clks are
> used by the firmware and can't be turned off in Linux. If in the future we want
> to be able to turn them on and off, we'll need to add them to an OP-TEE device
> node and have that driver manage the clks.
> 
> How that will work when a system doesn't enable the OP-TEE driver I'm not
> sure. We may need to develop some system whereby clks like this are handed
> from the clk controller to the consumer driver when it's enabled for further
> power managment, but if they're never handed off, they're kept on forever like
> is done here. Anyway, please resend with a note about why these are marked
> CLK_IS_CRITICAL.
 
I think there is some misunderstanding here, this patch sets those critical clocks
with CLK_IS_CRITICAL flag to let clock driver keep them always ON, as they are
critical clocks and system (Linux kernel, NOT include op-tee) can NOT run normally
if anyone of them is OFF.

The question about op-tee is, there might be some special clocks needed by op-tee,
for example, currently clk A, B and C are kept always ON for Linux kernel to run normally,
but when op-tee is executing, it might need clk D to be ON, so I think the clk D is needed
ONLY for op-tee, op-tee should have a driver or firmware to runtime ON/OFF clk D as needed.
Since I do NOT know what clocks op-tee needs, so I will leave them to be added by op-tee
owner, whoever enables op-tee, he should consider where to manage its special clocks,
either in clk driver or op-tee driver/firmware.

So do we still need to mention the op-tee related info in commit text? Actually, this patch
is just to replace those always-ON clocks in clks_init_on array with CLK_IS_CRITICAL flag.
Then no need to explicitly enable clocks in clks_init_on array and just rely on common clk
framework which will enable all clocks with CLK_IS_CRITICAL flag set, it will align with all
other i.MX SoCs clk driver.

Anson.