From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Kurtz Subject: Re: [PATCH 1/3] serial: 8250_early: Add earlycon support for AMD Carrizo / Stoneyridge Date: Wed, 14 Mar 2018 16:29:56 +0000 Message-ID: References: <20180314003655.12141-1-djkurtz@chromium.org> <20180314003655.12141-2-djkurtz@chromium.org> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: ricardo.ribalda@gmail.com Cc: adurbin@chromium.org, Greg Kroah-Hartman , jslaby@suse.com, marc_gonzalez@sigmadesigns.com, Doug Anderson , matt.redfearn@mips.com, Jeffy , linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-serial@vger.kernel.org Hi Ricardo, On Wed, Mar 14, 2018 at 4:54 AM Ricardo Ribalda Delgado < ricardo.ribalda@gmail.com> wrote: > Hi Daniel > On Wed, Mar 14, 2018 at 1:36 AM, Daniel Kurtz wrote: > > > > AMD Carrizo / Stoneyridge use a DesignWare 8250 UART that uses a 48 MHz > > input clock. > > > > Allow these platforms to set up this clock by specifying a kernel command > > line like: > > earlycon=amdcz,mmio32,0xfedc6000,115200 > If the port and the mode (mmio32) is always fixed, couldn't we just > add those two into > early_amdcz_setup? There are multiple memory mapped UARTs on at least the one chip I am aware of, specifying the address here chooses which port to use as the early console. In fact, the recommended way is to have firmware specify an ACPI SPCR table with OEMID="AMDCZ " (see https://patchwork.kernel.org/patch/10281307/) to configure proper access and address. With an SPCR table in place, the kernel command line just becomes "earlycon", with no parameters. -Dan