Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
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 <andriy.shevchenko@linux.intel.com>
To:     Daniel Kurtz <djkurtz@chromium.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     adurbin@chromium.org, linux-kernel@vger.kernel.org,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Len Brown <lenb@kernel.org>, Jiri Slaby <jslaby@suse.com>,
        Kees Cook <keescook@chromium.org>,
        Matthias Brugger <mbrugger@suse.com>,
        David Howells <dhowells@redhat.com>,
        Allen Pais <allen.lkml@gmail.com>, Sean Young <sean@mess.org>,
        Douglas Anderson <dianders@chromium.org>,
        Matt Redfearn <matt.redfearn@mips.com>,
        Jeffy Chen <jeffy.chen@rock-chips.com>,
        Marc Gonzalez <marc_gonzalez@sigmadesigns.com>,
        "open list:ACPI" <linux-acpi@vger.kernel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@vger.kernel.org>
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"
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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 <andriy.shevchenko@linux.intel.com>
Intel Finland Oy