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From: Stephen Boyd <>
To: Janek Kotas <>
Cc: "" <>,
	"" <>,
	"" <>,
	"" <>,
	"" <>,
	"" <>
Subject: Re: [PATCH 2/2] clk: Add Fixed MMIO clock driver
Date: Fri, 30 Nov 2018 00:58:30 -0800	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

Quoting Janek Kotas (2018-11-30 00:52:16)
>         We have a single register in a fixed location which contains 
>         the frequency of the main system clock.
>         This allows us to use the same image in emulation, FPGA
>         and simulation without any changes.
>         We usually don’t use a full bootloader, just a simple wrapper,
>         which initializes the necessary stuff and jumps to the kernel.
>     So the hardware team has decided to throw a frequency register in there?
>     Alright! Does that fixed rate clk generate its fixed rate from some
>     other clk? I’m curious if this fixed rate clk has a parent source.
> It depends, in simulation and emulation we can just generate 
> a clock source with a given frequency.
> On FPGA it’s usually an external oscillator, sometimes a fixed PLL.
> The driver is not intended to be used in full, complex SoCs.

Ok, sounds like it isn't worth modeling this then.

>     It would also be good to make sure that any clks registered from this
>     driver can't be populated from regions of memory like DDR. Can you
>     confirm? I think it will fail, but it would be worth checking

Please try this.

>     Yes I'd prefer a platform driver unless there's some reason it can't be
>     done. We may need to have both in case this needs to be populated very
>     early, but if that isn’t the case then just a platform driver for now.
> I played with it a bit, and it and it looks like I need both.
> We use this clock source with some of our components, 
> and for some of them the platform driver was initialized too late.

Ok. So do both then.

  parent reply	other threads:[~2018-11-30  8:58 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-14 15:24 Janek Kotas
2018-11-14 22:19 ` Stephen Boyd
2018-11-15  8:27   ` Janek Kotas
2018-11-29 22:29     ` Stephen Boyd
     [not found]       ` <>
2018-11-30  8:58         ` Stephen Boyd [this message]
     [not found]           ` <>
2018-11-30 18:56             ` Stephen Boyd

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