Re: [PATCH v2 4/4] scsi: ufs: probe and init of variant driver from the platform device

From: Rob Herring <robherring2@gmail.com>
To: Dov Levenglick <dovl@codeaurora.org>
Cc: Yaniv Gardi <ygardi@codeaurora.org>,
	Akinobu Mita <akinobu.mita@gmail.com>,
	merez@qti.qualcomm.com, dovl@qti.qualcomm.com,
	Jej B <james.bottomley@hansenpartnership.com>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-scsi@vger.kernel.org,
	linux-arm-msm <linux-arm-msm@vger.kernel.org>,
	Santosh Y <santoshsy@gmail.com>,
	linux-scsi-owner@vger.kernel.org,
	Subhash Jadavani <subhashj@codeaurora.org>,
	Paul Bolle <pebolle@tiscali.nl>,
	Gilad Broner <gbroner@codeaurora.org>,
	Rob Herring <robh+dt@kernel.org>, Pawel Moll <pawel.moll@arm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Ian Campbell <ijc+devicetree@hellion.org.uk>,
	Kumar Gala <galak@codeaurora.org>,
	Vinayak Holikatti <vinholikatti@gmail.com>,
	"James E.J. Bottomley" <jbottomley@odin.com>,
	Dolev Raviv <draviv@codeaurora.org>,
	Christoph Hellwig <hch@lst.de>,
	Sujit Reddy Thumma <sthumma@codeaurora.org>,
	Raviv Shvili <rshvili@codeaurora.org>,
	Sahitya Tummala <stummala@codeaurora.org>,
	"open list:OPEN FIRMWARE AND..." <devicetree@vger.kernel.org>
Subject: Re: [PATCH v2 4/4] scsi: ufs: probe and init of variant driver from the platform device
Date: Tue, 9 Jun 2015 07:53:28 -0500	[thread overview]
Message-ID: <CAL_Jsq+SWq9=xTjVvQH2tMoq=g_rjk44A7T4TMFKvDiUp_ahCg@mail.gmail.com> (raw)
In-Reply-To: <bfade46f9d953e10240acb835105b81d.squirrel@www.codeaurora.org>

On Tue, Jun 9, 2015 at 12:53 AM, Dov Levenglick <dovl@codeaurora.org> wrote:
>> On Sun, Jun 7, 2015 at 10:32 AM,  <ygardi@codeaurora.org> wrote:
>>>> 2015-06-05 5:53 GMT+09:00  <ygardi@codeaurora.org>:

[...]

>>> If ufshcd-pltfrm driver is loaded before ufs-qcom, (what actually
>>> happens
>>> always), then the calling to of_platform_populate() which is added,
>>> guarantees that ufs-qcom probe will be called and finish, before
>>> ufshcd_pltfrm probe continues.
>>> so ufs_variant device is always there, and ready.
>>> I think it means we are safe - since either way, we make sure ufs-qcom
>>> probe will be called and finish before dealing with ufs_variant device
>>> in
>>> ufshcd_pltfrm probe.
>>
>> This is due to the fact that you have 2 platform drivers. You should
>> only have 1 (and 1 node). If you really think you need 2, then you
>> should do like many other common *HCIs do and make the base UFS driver
>> a set of library functions that drivers can use or call. Look at EHCI,
>> AHCI, SDHCI, etc. for inspiration.
>
> Hi Rob,
> We did look at SDHCI and decided to go with this design due to its
> simplicity and lack of library functions. Yaniv described the proper flow
> of probing and, as we understand things, it is guaranteed to work as
> designed.
>
> Furthermore, the design of having a subcore in the dts is used in the
> Linux kernel. Please have a look at drivers/usb/dwc3 where - as an example
> - both dwc3-msm and dwc3-exynox invoke the probing function in core.c
> (i.e. the shared underlying Synopsys USB dwc3 core) by calling
> of_platform_populate().

That binding has the same problem. Please don't propagate that. There
is no point in a sub-node in this case.

> Do you see a benefit in the SDHCi implementation?

Yes, it does not let the kernel driver design dictate the hardware description.

Rob