linux-kernel - Re: [PATCH] amba: make amba

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Message-ID: <56e29159-3ebb-425a-9bd6-cb66484d7738@linux.dev>
Date: Mon, 26 Aug 2024 18:08:11 +0800
From: Kunwu Chan <kunwu.chan@...ux.dev>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: linux@...linux.org.uk, krzk@...nel.org, andi.shyti@...nel.org,
 robh@...nel.org, gregkh@...uxfoundation.org, suzuki.poulose@....com,
 rmk+kernel@...linux.org.uk, linux-kernel@...r.kernel.org,
 Kunwu Chan <chentao@...inos.cn>
Subject: Re: [PATCH] amba: make amba_bustype constant

On 2024/8/23 21:48, Andy Shevchenko wrote:
> On Fri, Aug 23, 2024 at 02:42:03PM +0800, Kunwu Chan wrote:
>> From: Kunwu Chan <chentao@...inos.cn>
>>
>> Since commit d492cc2573a0 ("driver core: device.h: make struct
>> bus_type a const *"), the driver core can properly handle constant
>> struct bus_type, move the amba_bustype variable to be a constant
>> structure as well, placing it into read-only memory which can not be
>> modified at runtime.
> ...
>
>> -extern struct bus_type amba_bustype;
>> +extern const struct bus_type amba_bustype;
> Can we actually hide this from the outside, i.e. make it static in the C file,
> and introduce the dev_is_amba() helper instead?
>
> P.S. You may look at the PNP bus case (some of the latest patches there)

I found it problematic in the process of making changes.

There have some usage of amba_bustype outside the AMBA code ,i.e: 
https://elixir.bootlin.com/linux/v6.10.4/source/drivers/iommu/iommu.c#L155

So, If we make the amba_bustype inside the AMBA code, the outside cannot 
access.

If only internal access is allowed, it will compile and report an error, 
how should I modify it next, and any suggestions?

-- 
Thanks,
   Kunwu.Chan