linux-kernel - Re: Kconfig fails: big select-based circular dependency

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Date:	Thu, 12 Jun 2014 12:31:19 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	linux-kernel@...r.kernel.org
Subject: Re: Kconfig fails: big select-based circular dependency

On Thursday 12 June 2014 10:47:45 Russell King - ARM Linux wrote:
> If no one responds, I'll assume that no one is interested, and I'll
> just create a pile of patches removing a bunch of these idiotic select
> statements at random to break this loop.

I missed the original mail, and I don't remember seeing this particular
dependency chain.

> On Sat, Jun 07, 2014 at 10:09:44AM +0100, Russell King - ARM Linux wrote:
> > This is getting silly:
> > 
> > scripts/kconfig/conf --silentoldconfig Kconfig
> > drivers/dma/Kconfig:5:error: recursive dependency detected!
> > drivers/dma/Kconfig:5:  symbol DMADEVICES is selected by SAMSUNG_DMADEV

The 'select DMADEVICES' from plat-samsung/Kconfig is certainly wrong,
we shouldn't do that, but I'd do some extended build regression tests
to ensure that it doesn't cause other problems.

I'll have a look.

> > arch/arm/plat-samsung/Kconfig:412:      symbol SAMSUNG_DMADEV is selected by S3C64XX_PL080
> > arch/arm/mach-s3c64xx/Kconfig:20:       symbol S3C64XX_PL080 is selected by SPI_S3C64XX
> > drivers/spi/Kconfig:429:        symbol SPI_S3C64XX depends on SPI
> > drivers/spi/Kconfig:8:  symbol SPI is selected by DRM_PANEL_LD9040

'select SPI' is also really bad. This seems trivial to replace with
'depends on SPI'. This is the only driver that uses select here.

> > drivers/gpu/drm/panel/Kconfig:19:       symbol DRM_PANEL_LD9040 depends on DRM_PANEL
> > drivers/gpu/drm/panel/Kconfig:1:        symbol DRM_PANEL is selected by DRM_IMX_LDB
> > drivers/staging/imx-drm/Kconfig:35:     symbol DRM_IMX_LDB depends on MFD_SYSCON
> > drivers/mfd/Kconfig:722:        symbol MFD_SYSCON is selected by POWER_RESET_KEYSTONE

We have 10 drivers doing 'select MFD_SYSCON' and 9 drivers doing
'depends on MFD_SYSCON'. Either one would work if we did those consistently,
here the problem is really mixing the two.

> > drivers/power/reset/Kconfig:76: symbol POWER_RESET_KEYSTONE depends on POWER_SUPPLY
> > drivers/power/Kconfig:1:        symbol POWER_SUPPLY is selected by HID_SONY
> > drivers/hid/Kconfig:622:        symbol HID_SONY depends on NEW_LEDS
> > drivers/leds/Kconfig:8: symbol NEW_LEDS is selected by BACKLIGHT_ADP8860

Here, it's much clearer: everything other than HID_SONY uses
'select NEW_LEDS', and so should this driver.

> > drivers/video/backlight/Kconfig:327:    symbol BACKLIGHT_ADP8860 depends on BACKLIGHT_CLASS_DEVICE
> > drivers/video/backlight/Kconfig:156:    symbol BACKLIGHT_CLASS_DEVICE is selected by FB_MX3
> > drivers/video/fbdev/Kconfig:2333:       symbol FB_MX3 depends on MX3_IPU
> > drivers/dma/Kconfig:121:        symbol MX3_IPU depends on DMADEVICES
> > 
> > This is a good illustration why the select disease is truely bad...

Definitely.

	Arnd
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