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

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Message-ID: <Zs3Wt5xkFOiuH-iP@smile.fi.intel.com>
Date: Tue, 27 Aug 2024 16:37:59 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Kunwu Chan <kunwu.chan@...ux.dev>
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 Tue, Aug 27, 2024 at 03:45:31PM +0800, Kunwu Chan wrote:
> On 2024/8/26 18:40, Andy Shevchenko wrote:
> > On Mon, Aug 26, 2024 at 06:08:11PM +0800, Kunwu Chan wrote:
> > > On 2024/8/23 21:48, Andy Shevchenko wrote:
> > > > On Fri, Aug 23, 2024 at 02:42:03PM +0800, Kunwu Chan wrote:

...

> > > > > -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.
> > Yes, that's the idea.
> > 
> > > If only internal access is allowed, it will compile and report an error, how
> > > should I modify it next, and any suggestions?

(1) vvv

> > Make it patch series:
> > 1) patch that introduces exported function called dev_is_amba() (1 patch);
> > 2) convert user-by-user (N patches);
> > 3) hide the bus type and make it constant.

(1) ^^^

> Here[1] have many use of  amba_bustype directly outside the drivers/amba

Yes.

> When I try to hide the amba_bustype by move the extern from
> include/linux/amba to drivers/amba,
> 
> we find some errors: "error: use of undeclared identifier amba_bustype".

Yes, that's why I put (1) to how solve this as we usually do in the Linux
kernel.

-- 
With Best Regards,
Andy Shevchenko