linux-kernel - Re: [PATCH v5 RESEND 4/5] ARM: amba: Move reading of periphid to amba

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Date:	Mon, 15 Feb 2016 17:52:50 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Marek Szyprowski <m.szyprowski@...sung.com>
Cc:	linux-samsung-soc@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Tomeu Vizoso <tomeu.vizoso@...labora.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Dan Williams <dan.j.williams@...el.com>,
	Kukjin Kim <kgene@...nel.org>,
	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [PATCH v5 RESEND 4/5] ARM: amba: Move reading of periphid to
 amba_match()

On Wed, Feb 10, 2016 at 11:47:29AM +0100, Marek Szyprowski wrote:
> From: Tomeu Vizoso <tomeu.vizoso@...labora.com>
> 
> Reading the periphid when the Primecell device is registered means that
> the apb pclk must be available by then or the device won't be registered
> at all.
> 
> By reading the periphid in amba_match() we can return -EPROBE_DEFER if
> the apb pclk isn't there yet and the device will be retried later.

I've just realised, we can't do this.  We need to read the peripheral
ID at registration time, because that's published to userspace via
(a) a sysfs attribute, and (b) as part of the uevent, which will be
used by udev to locate the driver module.

So, this will have the side effect of breaking systems which have
AMBA primecell devices configured as modules.

Sorry, I can't apply this.  We can't regress existing platforms for
the sake of introducing new platforms to this code.

-- 
RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/
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