linux-kernel - RE: [PATCH 2/2] clk: imx: imx7d: remove clks_init

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Date:   Fri, 31 Aug 2018 01:40:21 +0000
From:   Anson Huang <anson.huang@....com>
To:     Stephen Boyd <sboyd@...nel.org>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mturquette@...libre.com" <mturquette@...libre.com>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        Fabio Estevam <fabio.estevam@....com>,
        Peng Fan <peng.fan@....com>, Rob Herring <robh@...nel.org>
CC:     dl-linux-imx <linux-imx@....com>
Subject: RE: [PATCH 2/2] clk: imx: imx7d: remove clks_init_on array

Hi, Stephen

Anson Huang
Best Regards!


> -----Original Message-----
> From: Stephen Boyd <sboyd@...nel.org>
> Sent: Friday, August 31, 2018 9:29 AM
> To: kernel@...gutronix.de; linux-arm-kernel@...ts.infradead.org;
> linux-clk@...r.kernel.org; linux-kernel@...r.kernel.org;
> mturquette@...libre.com; s.hauer@...gutronix.de; shawnguo@...nel.org;
> Anson Huang <anson.huang@....com>; Fabio Estevam
> <fabio.estevam@....com>; Peng Fan <peng.fan@....com>; Rob Herring
> <robh@...nel.org>
> Cc: dl-linux-imx <linux-imx@....com>
> Subject: RE: [PATCH 2/2] clk: imx: imx7d: remove clks_init_on array
> 
> Quoting Peng Fan (2018-08-12 18:15:41)
> > Hi Anson,
> >
> > > > > -----Original Message-----
> > > > > From: Anson Huang
> > > > > Sent: 2018年8月8日 12:39
> > > > > To: shawnguo@...nel.org; s.hauer@...gutronix.de;
> > > > > kernel@...gutronix.de; Fabio Estevam <fabio.estevam@....com>;
> > > > > mturquette@...libre.com; sboyd@...nel.org;
> > > > > linux-arm-kernel@...ts.infradead.org;
> > > > > linux-clk@...r.kernel.org; linux-kernel@...r.kernel.org
> > > > > Cc: dl-linux-imx <linux-imx@....com>
> > > > > Subject: [PATCH 2/2] clk: imx: imx7d: remove clks_init_on array
> > > > >
> > > > > Clock framework will enable those clocks registered with
> > > > > CLK_IS_CRITICAL flag, so no need to have clks_init_on array
> > > > > during clock
> > > > initialization now.
> > > >
> > > > Will it be more flexible to parse dts saying "critical-clocks = <xxx>"
> > > > or "init-on-arrary=<xxx>"
> > > > and enable those clocks?
> > >
> > > Parsing the clocks arrays from dtb is another way of enabling
> > > critical clocks, but for current i.MX6/7 platforms, we implement it
> > > in same way as most of other SoCs, currently I did NOT see any
> > > necessity of putting them in dtb, just adding flag during clock
> > > registering is more simple, if there is any special requirement for
> > > different clocks set to be enabled, then we can add support to enable the
> method of parsing critical-clocks from dtb. Just my two cents.
> >
> > Thinking about OP-TEE want to use one device, but it's clocks are
> > registered by Linux, because there is no module in Linux side use it,
> > it will shutdown the clock, which cause OP-TEE could not access the device.
> >
> > Then people have to modify clk code to add CLK_IS_CRITICAL flag to
> > make sure the clocks are not shutdown by Linux.
> >
> > However adding a new property in clk node and let driver code parse
> > the dts, there is no need to modify clk driver code when OP-TEE needs
> another device clock.
> >
> 
> If OP-TEE needs linux to keep things on then why can't the OP-TEE driver in
> Linux probe, acquire clocks, and keep the clks enabled forever?
 
Yes, I agree with you, OP-TEE should maintain its clocks when OP-TEE is enabled.

This is ONLY a concern raised by Peng, all platforms' current clock driver does NOT consider
this case, so I think this patch should be fine for now? Thanks.

Anson.