RE: [PATCH v1 0/2] Common SerDes driver for TI's Keystone Platforms

[Kwok, WingMan]

Hello,

> -----Original Message-----
> From: KISHON VIJAY ABRAHAM
> Sent: Thursday, October 15, 2015 3:22 PM
> To: Russell King - ARM Linux; Kwok, WingMan
> Cc: robh+dt@xxxxxxxxxx; pawel.moll@xxxxxxx; mark.rutland@xxxxxxx;
> ijc+devicetree@xxxxxxxxxxxxxx; galak@xxxxxxxxxxxxxx; Quadros, Roger;
> Karicheri, Muralidharan; bhelgaas@xxxxxxxxxx; ssantosh@xxxxxxxxxx;
> devicetree@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux-
> pci@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [PATCH v1 0/2] Common SerDes driver for TI's Keystone Platforms
> 
> Hi,
> 
> On Thursday 15 October 2015 10:21 PM, Russell King - ARM Linux wrote:
> > On Thu, Oct 15, 2015 at 10:25:43AM -0400, WingMan Kwok wrote:
> >> On TI's Keystone platforms, several peripherals such as the
> >> gbe ethernet switch, 10gbe ethether switch and PCIe controller
> >> require the use of a SerDes for converting SoC parallel data into
> >> serialized data that can be output over a high-speed electrical
> >> interface, and also converting high-speed serial input data
> >> into parallel data that can be processed by the SoC.  The
> >> SerDeses used by those peripherals, though they may be different,
> >> are largely similar in functionality and setup.
> >
> > Given that serdes is not specific to TI, should this be specific to
> > TI, or should there be an effort to come up with something which
> > everyone who has serdes links can make use of?
> >
> > Serdes comes in multiple different forms: PCIe, 1G SGMII ethernet,
> > 1000base-X ethernet, 10g ethernet, SATA... I'd hate to see a
> > plethora of SoC specific stuff for this.
> 
> Generally every SoC use it's own serdes and the programming required is
> different for different SoCs. Each of them have their own register map
> and clock programming/regulator programming/reset programming are all
> different.
> 
> However most SoC vendors use the same PHY/SerDes IP to be used by
> multiple controllers like PCIe/SATA/USB in a single SoC and a single PHY
> driver is used for programming all these PHYs.
> 

Thanks so much for the clarifications.

> Thanks
> Kishon
> 

Regards,
WingMan

> >
> > When serdes is combined with SFP cages, the situation becomes much
> > more fun, because the serdes link then needs to become hotpluggable
> > (SFP modules are designed to be hotplugged) which means you have to
> > be able to switch between (at least) 1G SGMII and 1000base-X modes,
> > and probably 10G mode as well.  There's even a SFP module that has
> > a SATA connector on it, though I believe there's no standard for
> > that, and it's more a hardware hack.
> >
> > I've been working in this area but from the Ethernet side on an
> > Armada 38x based board which has a SFP cage on it, though it's
> > slightly simpler there because there is no support (or I believe
> > any desire) to reconfigure the serdes lanes between PCI, ethernet
> > and SATA - that's all setup and initialised for us by uboot.
> >