linux-kernel - Re: [PATCH v3 13/13] scsi: ufs: Add exynos ufs platform data

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Message-ID: <14885029.SsJgQkuPcG@wuerfel>
Date:	Mon, 05 Oct 2015 11:06:59 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Alim Akhtar <alim.akhtar@...sung.com>
Cc:	kbuild test robot <lkp@...el.com>, kbuild-all@...org,
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
	JBottomley@...n.com, vinholikatti@...il.com,
	amit.daniel@...sung.com, essuuj@...il.com,
	devicetree@...r.kernel.org, Rob Herring <robh@...nel.org>
Subject: Re: [PATCH v3 13/13] scsi: ufs: Add exynos ufs platform data

On Monday 05 October 2015 13:44:29 Alim Akhtar wrote:
> CCing Rob Herring,
> 
> Hi Arnd,
> 
> On 10/01/2015 04:59 PM, Arnd Bergmann wrote:
> > On Thursday 01 October 2015 18:46:34 kbuild test robot wrote:
> >> [auto build test results on v4.3-rc3 -- if it's inappropriate base, please ignore]
> >>
> >> config: x86_64-allmodconfig (attached as .config)
> >> reproduce:
> >>          git checkout 6e153e3bf7c68b019e987c5a0ffadebd9c7d4fbb
> >>          # save the attached .config to linux build tree
> >>          make ARCH=x86_64
> >>
> >> All error/warnings (new ones prefixed by >>):
> >>
> >>>> ERROR: "ufs_hba_exynos_ops" [drivers/scsi/ufs/ufshcd-pltfrm.ko] undefined!
> >>
> >>
> >
> > Ah, this seems to be a case of layering violation. It would be best to
> > restructure the code so that the exynos driver registers a platform_driver
> > by itself for the respective DT compatible string, and then calls
> > into the common code from its probe function, rather than having the
> > generic driver know about the specific backends.
> >
> > That approach will also make the generic driver more scalable as we
> > add further chip-specific variations, and matches what we do in other
> > drivers.
> >
> 
> Looks like some discussions on ufs variant driver probe method happened 
> here [1] few months back.
> [1]-> https://lkml.org/lkml/2015/6/3/180

Hmm, too bad we didn't catch it then, it's much more work to fix now.

> And since ufshcd-pltfrm is already a platform_driver, so I just add a 
> platform data for the variant driver.
> I should have add a IS_ENABLED for it to avoid the compilation error for 
> other ARCH.

I still think we should do this properly here. From looking at the qcom
driver, it seems to me that the integration there was done in a way that
could not work at all:

$ git grep -w ufs_hba_qcom_vops
drivers/scsi/ufs/ufs-qcom.c: * struct ufs_hba_qcom_vops - UFS QCOM specific variant operations
drivers/scsi/ufs/ufs-qcom.c:static const struct ufs_hba_variant_ops ufs_hba_qcom_vops = {
drivers/scsi/ufs/ufs-qcom.c:EXPORT_SYMBOL(ufs_hba_qcom_vops);

In short, nothing references the ufs_hba_qcom_vops symbol, so the driver
is never used, and if it did, it would not work for ufs being built-in
beause the symbol is marked 'static'.

Please do the samsung front-end as I suggested and send a patch to
convert the qcom front-end the same way. No need to test that one
as the current approach doesn't work.

	Arnd
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