From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [PATCH v3 0/2] Common SerDes driver for TI's Keystone Platforms Date: Fri, 23 Oct 2015 11:17:06 +0200 Message-ID: <3702663.07h6YO0UjY@wuerfel> References: <1445432201-16007-1-git-send-email-w-kwok2@ti.com> <56295B9E.9030201@ti.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Return-path: In-Reply-To: Sender: linux-pci-owner@vger.kernel.org To: Loc Ho Cc: Murali Karicheri , Russell King - ARM Linux , KISHON VIJAY , WingMan Kwok , Rob Herring , pawel.moll@arm.com, Mark Rutland , Ian Campbell , galak@codeaurora.org, rogerq@ti.com, bhelgaas@google.com, ssantosh@kernel.org, "devicetree@vger.kernel.org" , Linux Kernel Mailing List , linux-pci@vger.kernel.org, "linux-arm-kernel@lists.infradead.org" List-Id: devicetree@vger.kernel.org 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