linux-kernel - Re: [PATCH 06/10] ARM: mach-airoha: Rework support and directory structure

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Message-ID: <3611feaa-9c89-b580-6266-c12cf048f56a@ti.com>
Date:   Thu, 13 Jul 2023 13:44:10 -0500
From:   Andrew Davis <afd@...com>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
CC:     Baruch Siach <baruch@...s.co.il>,
        Vladimir Zapolskiy <vz@...ia.com>,
        Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Linus Walleij <linus.walleij@...aro.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 06/10] ARM: mach-airoha: Rework support and directory
 structure

On 5/15/23 11:31 AM, Russell King (Oracle) wrote:
> On Mon, May 15, 2023 at 11:02:30AM -0500, Andrew Davis wrote:
>> Having a platform need a mach-* directory should be seen as a negative,
>> it means the platform needs special non-standard handling. ARM64 support
>> does not allow mach-* directories at all. While we may not get to that
>> given all the non-standard architectures we support, we should still try
>> to get as close as we can and reduce the number of mach directories.
>>
>> The mach-airoha/ directory, and files within, provide just one "feature":
>> having the kernel print the machine name if the DTB does not also contain
>> a "model" string (which they always do). To reduce the number of mach-*
>> directories let's do without that feature and remove this directory.
> 
> I'm guessing this is copy-n-pasted description. However:
>> -static const char * const airoha_board_dt_compat[] = {
>> -	"airoha,en7523",
>> -	NULL,
>> -};
>> -
>> -DT_MACHINE_START(MEDIATEK_DT, "Airoha Cortex-A53 (Device Tree)")
>> -	.dt_compat	= airoha_board_dt_compat,
>> -MACHINE_END
> 
> If this is actually used, then it will have the effect of providing a
> "machine" that has both l2c_aux_mask and l2c_aux_val as zero, whereas
> the default one has l2c_aux_mask set to ~0.
> 

Given we set l2c_aux_mask to ~0 as a default for "Generic" DT system I
had assumed this was safe, but no I cannot prove it for this board as
I don't have one.

I wonder if we should have some way to set this in DT, that would
let us drop some more MACHINE defines that exist only to set
the l2c_aux_val/mask..

> This has the effect of _not_ calling l2x0_of_init() - but you don't
> mention this. You probably should, and you should probably state why
> that is safe (assuming you've even realised you've made this change!)
> 

Reverse question, did the folks adding this support know this had
the effect of changing l2c_aux_mask from the default?

For now I'll resend this series with only the first 5 patches which
should be trivially safe. The later ones I can send after double
checking on l2x0_of_init().

Andrew