From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752764AbbJWJRa (ORCPT ); Fri, 23 Oct 2015 05:17:30 -0400 Received: from mout.kundenserver.de ([212.227.126.187]:57955 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751080AbbJWJRZ (ORCPT ); Fri, 23 Oct 2015 05:17:25 -0400 From: Arnd Bergmann 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" 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> User-Agent: KMail/4.11.5 (Linux/3.16.0-10-generic; KDE/4.11.5; x86_64; ; ) In-Reply-To: References: <1445432201-16007-1-git-send-email-w-kwok2@ti.com> <56295B9E.9030201@ti.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" X-Provags-ID: V03:K0:KzyNEiiGL4yGC1FVz5YFLNgtnaheG7au1LIo2VXe4VAvrLCGpGj ZMfhCU2Znklu49mjTyD59rGO+QB84MjFRJpqpPXMze6qDNi32kylw79JdXT8WxBjU1zWE+4 C6P0CSfJbumdPQ+iu0Ew1cftljeklduOsDOOfZtIoSzoGMwpMH43HJkPlsAAEGEwkYUVLIY 9swDmcCQOM9sPpq5398gQ== X-UI-Out-Filterresults: notjunk:1;V01:K0:E3LTO3qNUok=:kXG2ghUr9eTxUGe1hbwnrw PjglC6QMRH4iWc3Df9XN23MknH1Q3nt/IUVOdlJhwaxxko5epJsfOieGoTrqz7IPjweAgEsqu oyVQ4vuSXjGPgylaYSm3yVw6Q7XLd4NpEKnPldayYAo/y6nmjSJiuDRtpC7qJkkiEzM8NkzeS 74Dabaq7FgPQiWfBMYJ84SkS6Hp8dswl1ctlfwMUQ+7LktdZjstStnNdS1YJxY0gp9A0GL4wS 3kgAKdUZSS6w/tDO8ZLOcAYNzY/gJPnIOYAEuYB1jx18lfrfOLOmelcwFbc8MElEdyrYAKy4G TzQusBM3AoOLi6CfwI/NkjYOm2xzVr4RoOdgW0XfC2GovGQmhR0uVSAwtd7g1RfyHKa5QqvW5 Dr5flXAFkkb4kEQjgwhNmV9XoCeLka/FwD9MVjaEvA+8hkDcxEjOlEkjM18DYrq3co3rn3hCq MlWyM/cN4j0yBx3YdjcQvGFQJdRRLzXd3x7P7DRf0hxArNColYUSe1t42mc8/dtJ2Ie0nMV3H ttVrInHTN4EC+xe6FpKmNxioVDqMI45Uwz4m+hfyI//li67SC8256Ed/9wKN2cQWxv+zpwK6y ksJmL5Zqm32Q8riqbZE8X8OnAdMKnlC0S/tyRYJLoS8G0OVKPjUtfYggnShrZQw6mWMMoglC3 /cWibDJZ53E2EJKPBKaUNb2/Vfe6327hqP5eYAkLXxjv6k8kFjdVMMT2WotBe/G+gzhmPnm3e Zg357CdBKrOwzvtU Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@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