linux-kernel - Re: [PATCH 1/2] socfpga: hotplug: put cpu1 in wfi

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Date:	Thu, 02 Oct 2014 14:18:09 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Pavel Machek <pavel@...x.de>,
	Dinh Nguyen <dinguyen@...nsource.altera.com>,
	linux@....linux.org.uk, atull <atull@...nsource.altera.com>,
	yvanderv@...nsource.altera.com, linux-kernel@...r.kernel.org,
	delicious.quinoa@...il.com
Subject: Re: [PATCH 1/2] socfpga: hotplug: put cpu1 in wfi

On Thursday 02 October 2014 01:16:46 Pavel Machek wrote:
> > > 
> > > struct socfpga_reset_manager {
> > >         u32     status;
> > >         u32     ctrl;
> > >         u32     counts;
> > >         u32     padding1;
> > >         u32     mpu_mod_reset;
> > >         u32     per_mod_reset;
> > >         u32     per2_mod_reset;
> > >         u32     brg_mod_reset;
> > > };
> > > 
> > > from u-boot. Unlike macros, structs have advantages that typos lead to
> > > easier-to-see failure modes... (And they are easier to read/parse,
> > > too).
> > > 
> > 
> > Copying from uboot sounds good, but I already know that the CPU reset
> > offset is different for our next SOC, Arria 10. The Arria 10 SOC should
> > still be able to use the same MSL as Cyclone5 and Arria5, but with a few
> > differences. One of them being, the CPU1 reset offset is at 0x20 instead
> > of 0x10. So I think having a macro for this one register is a bit
> > cleaner than having to define a whole new struct for Arria10.
> 
> I don't think "whole new struct" is a problem. At least it will be
> plain to see what changed (which will get easily lost in ifdefs.
> 
> struct cyclone5_reset_manager {
>         struct socfpga_reset_manager common;
>         u32 brg_mod_reset;
> }
> 
> struct aria10_reset_manager {
>         struct socfpga_reset_manager common;
>         char filler[0x10];
>         u32 brg_mod_reset;
> }
> 
> if (of_machine_is_compatible("altr,socfpga-arria10"))
>         __raw_writel(0, (struct cyclone5_reset_manager *) rst_manager_base_addr->brg_mod_reset));
> else
>         __raw_writel(0, (struct aria10_reset_manager *) rst_manager_base_addr->brg_mod_reset));
> 
> ...does not sound that bad. (And you'll need some nice solution for
> u-boot, anyway...)

I think it would be better to just add more fields and access a different
field based on the SoC type than cast the structs around.

Also, never use __raw_writel unless you know exactly what you are doing.
This should use writel, or possibly writel_relaxed.

Finally, don't sprinkle of_machine_is_compatible() checks all over the
place. Make the decision once when you initially probe the machine.

	Arnd
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