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

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Date:   Mon, 8 Oct 2018 08:34:59 +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>,
        Jerome Forissier <jerome.forissier@...aro.org>,
        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



Anson Huang
Best Regards!


> -----Original Message-----
> From: Stephen Boyd <sboyd@...nel.org>
> Sent: Monday, October 8, 2018 3:41 PM
> 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>; Jerome Forissier <jerome.forissier@...aro.org>;
> 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 Anson Huang (2018-09-03 00:20:53)
> > > > On 08/31/2018 03:29 AM, Stephen Boyd wrote:
> > > > > 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?
> > > >
> > > > Sounds reasonable, but how could this be done without introducing
> > > > platform-specific stuff in the OP-TEE driver?
> > > >
> > >
> > > Why is that a goal?
> >
> > I do NOT think we should consider such case in this patch series,
> > whatever OP-TEE needs for its own feature, it should do necessary operations
> either in its driver or somewhere else by adding new patch.
> >
> 
> 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? And I think if op-tee has such requirement,
can we have another patch to cover it? 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?

Anson.