linux-kernel - Re: [PATCH v3 0/2] Common SerDes driver for TI's Keystone Platforms

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Date:	Fri, 23 Oct 2015 10:25:54 -0400
From:	Murali Karicheri <m-karicheri2@...com>
To:	Arnd Bergmann <arnd@...db.de>, Loc Ho <lho@....com>
CC:	Russell King - ARM Linux <linux@....linux.org.uk>,
	KISHON VIJAY <kishon@...com>, WingMan Kwok <w-kwok2@...com>,
	Rob Herring <robh+dt@...nel.org>, <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	<galak@...eaurora.org>, <rogerq@...com>, <bhelgaas@...gle.com>,
	<ssantosh@...nel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	<linux-pci@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3 0/2] Common SerDes driver for TI's Keystone Platforms

On 10/23/2015 05:17 AM, Arnd Bergmann wrote:
> On Thursday 22 October 2015 15:27:05 Loc Ho wrote:
>>>
>>> phy-xgene.c
>>> -----------
>>>
>>> Looking at other drivers under drivers/phy, I could find phy-xgene.c which
>>> is close Keystone SerDes driver (. This is called APM X-Gene Multi-Purpose
>>> PHY driver. It defines following mode per the driver code
>>>
>>>          MODE_SATA       = 0,    /* List them for simple reference */
>>>          MODE_SGMII      = 1,
>>>          MODE_PCIE       = 2,
>>>          MODE_USB        = 3,
>>>          MODE_XFI        = 4,
>>>
>>> But seems to support only MODE_SATA. From the code, it appears, this driver
>>> is expected to be enhanced in the future to support additional modes. I have
>>> copied the author to this email to participate in this discussion.
>>
>> Let me comment on this APM X-Gene driver. This driver is dead and
>> won't be supported in near or foreseeable future. And someday, it will
>> be ripped out. Based on experience, this solution (having PHY driver
>> in Linux) can't be supported across boards and etc as it is just too
>> much maintenance. And therefore, we followed Arnd B guidance and move
>> all this into the boot loader. From Linux or OS perspective, it only
>> cares about the interface in which its interface with. This is just
>> your reference and may be this will help you as well.
>
> This depends a lot on the use case. If the chip is only used on server
> parts that have a real firmware and you can deliver bug fixes for the
> firmware if necessary, it's always best to do as much of the setup as
> possible there, and let Linux see a simplified view of the hardware.
>
> However, for embedded systems that tend to ship with a minimal binary
> bootloader and no way to update that as an end-user, we rely on Linux
> to know about all the hardware that requires some form of setup, which
> is why we have all sorts of drivers and frameworks in the kernel that
> a server can easily ignore.
>
> While keystone can show up in servers that won't use this driver, my
> impression is that its main market is actually in embedded space.
It is in embedded space predominantly. From our experience, this has to 
be a Linux driver and moving this to boot loader doesn't make sense.

Murali
>
> 	Arnd
>


-- 
Murali Karicheri
Linux Kernel, Keystone
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