From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AG47ELve15oXBgkysvL+gZRIzfrmk9rpH5Uk98oDJH9kruYa5I++m2pyTfqS/10TSRzaLadaDOiC ARC-Seal: i=1; a=rsa-sha256; t=1521119105; cv=none; d=google.com; s=arc-20160816; b=RqvFQ0dq7AWF8WjzsDuCWUg2uQSKYec/2s+Vl9uAlxwepHCZprYAiMxJCinBAmc29+ USb/u1Mv8FAPKhzDMKTAPCilKVKVKpdp+1rJ/cWCKc4Dr17PSIeXrWmAChtTaq2W48aI YncYl7v1BTO0Sgyz31izBkg7hHkFIZW7k8/9TbSGcqNIKtqPDfSF73TdwuRYmcOvbow4 8W1VAcG3JSsHgqAdQCFFVex3DOiOqghXLm+qNG+uw+1dgu+JYGeUMm+x4+NlGoEXS2yK +G6IWp9oVcAztlXHPY7d2jETgCQdeAq8oAmmoUix80xjLuV1V6cEElM6v9Z+hPS2NLru iChw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=content-transfer-encoding:mime-version:organization:references :in-reply-to:date:cc:to:from:subject:message-id :arc-authentication-results; bh=h5ZfXodXpFvirbeON7/QXBeaTULv+ZQvXhN7VgNxsN4=; b=jqUBqQv0zdzRQIFBXwEPe2ELONGDStDKxJBlpVOjrWktgvG7GbftjElqYueFWEKKRT N1ICIy+XQbFnemtDi8VIzmJDuqK5enLoXhlHZKHYAh1LbfiP0dbfFj0axO8wOpyc5DLh OkZE28NnCA28vcqw8pSQttnOGaeBigH1j+aoKKnHcOo8NhfKTIZZkdNXVW6yN4HRzYHi MUP3j/hjHGfgEv0ooqd8ukcOGew+wUMYBvNhGn9Hap3KhBTR4LLPGl6CiQc0WQjmaDq3 9XM2mYGLtNqT9CBOAMql9iFXVfDBceA6lBdh2X1/xjAfbsa/IDyq+9UGI8RKN8Mjr7fr tUlQ== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: best guess record for domain of andriy.shevchenko@linux.intel.com designates 192.55.52.93 as permitted sender) smtp.mailfrom=andriy.shevchenko@linux.intel.com Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of andriy.shevchenko@linux.intel.com designates 192.55.52.93 as permitted sender) smtp.mailfrom=andriy.shevchenko@linux.intel.com X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.48,310,1517904000"; d="scan'208";a="211815975" Message-ID: <1521119068.10722.661.camel@linux.intel.com> Subject: Re: [PATCH v3 3/3] serial: core: Allow skipping old serial port initialization From: Andy Shevchenko To: Daniel Kurtz , Greg Kroah-Hartman Cc: adurbin@chromium.org, linux-kernel@vger.kernel.org, "Rafael J. Wysocki" , Len Brown , Jiri Slaby , Kees Cook , Matthias Brugger , David Howells , Allen Pais , Sean Young , Douglas Anderson , Matt Redfearn , Jeffy Chen , Marc Gonzalez , "open list:ACPI" , "open list:SERIAL DRIVERS" Date: Thu, 15 Mar 2018 15:04:28 +0200 In-Reply-To: <20180315020445.150604-4-djkurtz@chromium.org> References: <20180315020445.150604-1-djkurtz@chromium.org> <20180315020445.150604-4-djkurtz@chromium.org> Organization: Intel Finland Oy Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.26.5-1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1594871331983338334?= X-GMAIL-MSGID: =?utf-8?q?1595008986894225895?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Wed, 2018-03-14 at 20:04 -0600, Daniel Kurtz wrote: > The old_serial_port global array in 8250_core is supposed to hold an > entry > for each serial port on the system that cannot be discovered via a > standard enumeration mechanism (aka ACPI/PCI/DTS). The array is > populated > at compile-time from the value specified in the SERIAL_PORT_DFNS > macro. > This macro is defined in arch/serial.h. > > For x86, this macro is currently unconditionally initialized to supply > four ioport UARTs (0x3F8, 0x2F8, 0x3E8, 0x2E8). > > However, not all x86 CPUs have these four ioport UARTs. For example, > the > UARTs on AMD Carrizo and later are separate memory mapped Designware > IP > blocks. > > Fairly early in boot the console_initcall univ8250_console_init > iterates > over this array and installs these old UARTs into the global array > serial8250_ports. Further, it attempts to register them for use as > the console. In other words, if, for example, the kernel commandline > has > console=ttyS0, the console will be switched over to one of these > non-existent UARTs. Only later, when the real UART drivers are probed > and their devices are instantiated will the console switch back over > to > the proper UART. > > This is noticeable when using earlycon, since part of the serial > console > log will appear to disappear (when the bogus old takes over) and then > re-appear (when the real UART finally gets registered for the > console). > > The problem is even more noticable when *not* using earlycon, since in > this case the entire console output is missing, having been > incorrectly > played back to the non-existing serial port. > > Create a global variable to allow skipping old serial port > initialization > and wire it up to the AMDCZ ACPI SPCR quirk and the special amdcz > earlycon > setup handler. I don't like this approach at all. But unfortunately I have nothing to propose. Just felt like I have to share my opinion on this. -- Andy Shevchenko Intel Finland Oy