linux-kernel - Re: [PATCH] SPCR: check bit width for the 16550 UART

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Message-ID: <3a6193ef-ca86-c113-b09a-5d6c882137e2@redhat.com>
Date:   Mon, 5 Dec 2016 21:27:26 -0500
From:   Jon Masters <jcm@...hat.com>
To:     Duc Dang <dhdang@....com>
Cc:     Aleksey Makarov <aleksey.makarov@...aro.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        linux-acpi@...r.kernel.org, linux-serial@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Russell King <linux@....linux.org.uk>,
        Peter Hurley <peter@...leysoftware.com>,
        Mark Salter <msalter@...hat.com>,
        Graeme Gregory <graeme.gregory@...aro.org>,
        Len Brown <lenb@...nel.org>
Subject: Re: [PATCH] SPCR: check bit width for the 16550 UART

Hi Duc, all,

So after regenerating the initrd override (I must have fat fingered)
it is now detecting the correct bit width on boot (attached dmesg log).

HOWEVER while the console does come up, the use of "earlycon" on the
command line (with no parameters) doesn't result in the early SPCR
console coming up correctly. I see some garbled characters that
suggest the baud (or register access width) is off somewhere.

Here are the first few lines from my screen boot log:

EFI stub: Using DTB from configuration table
EFI stub: Exiting boot services and installing virtual address map...
^E^B^B^B<8A>r<A2><92><A2><92>ʺ<EA><81>console [ttyS0] enabled
[    1.424297] console [ttyS0] enabled
[    1.507860] bootconsole [uart0] disabled

Can you double check you've actually seen the SPCR used for earlycon,
as the machine was booting, and actually generating correct output?

Here's the SPCR override I am using on that machine:

/*
 * Intel ACPI Component Architecture
 * AML/ASL+ Disassembler version 20160527-64
 * Copyright (c) 2000 - 2016 Intel Corporation
 * 
 * Disassembly of SPCR.aml, Sat Dec  3 03:49:54 2016
 *
 * ACPI Data Table [SPCR]
 *
 * Format: [HexOffset DecimalOffset ByteLength]  FieldName : FieldValue
 */

[000h 0000   4]                    Signature : "SPCR"    [Serial Port Console Redirection table]
[004h 0004   4]                 Table Length : 00000050
[008h 0008   1]                     Revision : 02
[009h 0009   1]                     Checksum : 41
[00Ah 0010   6]                       Oem ID : "HPE   "
[010h 0016   8]                 Oem Table ID : "ProLiant"
[018h 0024   4]                 Oem Revision : 00001337
[01Ch 0028   4]              Asl Compiler ID : "INTL"
[020h 0032   4]        Asl Compiler Revision : 20160527

[024h 0036   1]               Interface Type : 00
[025h 0037   3]                     Reserved : 000000

[028h 0040  12]         Serial Port Register : [Generic Address Structure]
[028h 0040   1]                     Space ID : 00 [SystemMemory]
[029h 0041   1]                    Bit Width : 20
[02Ah 0042   1]                   Bit Offset : 00
[02Bh 0043   1]         Encoded Access Width : 00 [Undefined/Legacy]
[02Ch 0044   8]                      Address : 000000001C021000

[034h 0052   1]               Interrupt Type : 08
[035h 0053   1]          PCAT-compatible IRQ : 00
[036h 0054   4]                    Interrupt : 0000006D
[03Ah 0058   1]                    Baud Rate : 03
[03Bh 0059   1]                       Parity : 00
[03Ch 0060   1]                    Stop Bits : 01
[03Dh 0061   1]                 Flow Control : 02
[03Eh 0062   1]                Terminal Type : 01
[04Ch 0076   1]                     Reserved : 00
[040h 0064   2]                PCI Device ID : FFFF
[042h 0066   2]                PCI Vendor ID : FFFF
[044h 0068   1]                      PCI Bus : 00
[045h 0069   1]                   PCI Device : 00
[046h 0070   1]                 PCI Function : 00
[047h 0071   4]                    PCI Flags : 00000000
[04Bh 0075   1]                  PCI Segment : 00
[04Ch 0076   4]                     Reserved : 00000000

Raw Table Data: Length 80 (0x50)

  0000: 53 50 43 52 50 00 00 00 02 41 48 50 45 4A 43 4D  // SPCRP....AHPEJCM
  0010: 50 72 6F 4C 69 61 6E 74 01 00 00 00 49 4E 54 4C  // ProLiant....INTL
  0020: 27 05 16 20 0D 00 00 00 00 08 00 00 00 10 02 1C  // '.. ............
  0030: 00 00 00 00 08 00 6D 00 00 00 03 00 01 02 01 00  // ......m.........
  0040: FF FF FF FF 00 00 00 00 00 00 00 00 00 00 00 00  // ................

Jon.

-- 
Computer Architect | Sent from my Fedora powered laptop


View attachment "dmesg-4.9.0-rc7.ecam_jcm2+-m400-spcr-works.txt" of type "text/plain" (29464 bytes)