linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Stephen Boyd <sboyd@kernel.org>
To: Janek Kotas <jank@cadence.com>
Cc: "mark.rutland@arm.com" <mark.rutland@arm.com>,
	"mturquette@baylibre.com" <mturquette@baylibre.com>,
	"robh+dt@kernel.org" <robh+dt@kernel.org>,
	"linux-clk@vger.kernel.org" <linux-clk@vger.kernel.org>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/2] clk: Add Fixed MMIO clock driver
Date: Fri, 30 Nov 2018 00:58:30 -0800	[thread overview]
Message-ID: <154356831048.88331.9290972200429107619@swboyd.mtv.corp.google.com> (raw)
In-Reply-To: <76BDCB72-CC05-41D1-93A0-6D71CBD97651@global.cadence.com>

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]       ` <76BDCB72-CC05-41D1-93A0-6D71CBD97651@global.cadence.com>
2018-11-30  8:58         ` Stephen Boyd [this message]
     [not found]           ` <63A29785-D1AC-4B7C-952E-3A2E5799A21D@global.cadence.com>
2018-11-30 18:56             ` Stephen Boyd

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=154356831048.88331.9290972200429107619@swboyd.mtv.corp.google.com \
    --to=sboyd@kernel.org \
    --cc=devicetree@vger.kernel.org \
    --cc=jank@cadence.com \
    --cc=linux-clk@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mark.rutland@arm.com \
    --cc=mturquette@baylibre.com \
    --cc=robh+dt@kernel.org \
    --subject='Re: [PATCH 2/2] clk: Add Fixed MMIO clock driver' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).