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

[Arnd Bergmann]

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.

	Arnd
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