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

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Date:	Wed, 17 Feb 2016 08:52:36 +0100
From:	Marek Szyprowski <m.szyprowski@...sung.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
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()

Hello,

On 2016-02-15 18:52, Russell King - ARM Linux wrote:
> 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.

Then the only solution right now I see is to get back to v1:
http://lists.infradead.org/pipermail/linux-arm-kernel/2015-November/388199.html
which at least handles correctly device registration when power domain 
driver
is available. You pointed that the patch cannot be applied, because failure
of dev_pm_domain_attach() will be fatal for device registration. Right now
lack of such call is fatal for the whole system, so there is really not a
big difference. Please also note that amba_get_enable_pclk() calls 
clk_get(),
which also might return -EPROBE_DEFER, which already breaks device
registration the same way.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland