[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [PATCH v2 01/30] hw/arm/raspi: Use BCM2708 machine type with pre Dev

From: BALATON Zoltan
Subject: Re: [PATCH v2 01/30] hw/arm/raspi: Use BCM2708 machine type with pre Device Tree kernels
Date: Fri, 7 Feb 2020 23:19:44 +0100 (CET)
User-agent: Alpine 2.22 (BSF 395 2020-01-19)

On Fri, 7 Feb 2020, Philippe Mathieu-Daudé wrote:
On 2/6/20 1:21 PM, BALATON Zoltan wrote:
On Thu, 6 Feb 2020, Philippe Mathieu-Daudé wrote:
When booting without device tree, the Linux kernels uses the $R1
register to determine the machine type. The list of values is
registered at [1].

There are two entries for the Raspberry Pi:

- https://www.arm.linux.org.uk/developer/machines/list.php?mid=3138
 name: MACH_TYPE_BCM2708
 value: 0xc42 (3138)
 status: Active, not mainlined
 date: 15 Oct 2010

- https://www.arm.linux.org.uk/developer/machines/list.php?mid=4828
 name: MACH_TYPE_BCM2835
 value: 4828
 status: Active, mainlined
 date: 6 Dec 2013

QEMU always used the non-mainlined type MACH_TYPE_BCM2708.
The value 0xc43 is registered to 'MX51_GGC' (processor i.MX51), and
0xc44 to 'Western Digital Sharespace NAS' (processor Marvell 88F5182).

The Raspberry Pi foundation bootloader only sets the BCM2708 machine
type, see [2] or [3]:

133 9:
134     mov r0, #0
135     ldr r1, =3138       @ BCM2708 machine id
136     ldr r2, atags       @ ATAGS
137     bx  r4

U-Boot only uses MACH_TYPE_BCM2708 (see [4]):

25 /*
26  * 2835 is a SKU in a series for which the 2708 is the first or primary SoC,
27  * so 2708 has historically been used rather than a dedicated 2835 ID.
28  *
29  * We don't define a machine type for bcm2709/bcm2836 since the RPi Foundation 30  * chose to use someone else's previously registered machine ID (3139, MX51_GGC)
31  * rather than obtaining a valid ID:-/
32  *
33  * For the bcm2837, hopefully a machine type is not needed, since everything
34  * is DT.
35  */

While the definition MACH_BCM2709 with value 0xc43 was introduced in
a commit described "Add 2709 platform for Raspberry Pi 2" out of the
mainline Linux kernel, it does not seem used, and the platform is
introduced with Device Tree support anyway (see [5] and [6]).

Remove the unused values (0xc43 introduced in commit 1df7d1f9303aef
"raspi: add raspberry pi 2 machine" and 0xc44 in commit bade58166f4
"raspi: Raspberry Pi 3 support"), keeping only MACH_TYPE_BCM2708.

[1] https://www.arm.linux.org.uk/developer/machines/
[2] https://github.com/raspberrypi/tools/blob/920c7ed2e/armstubs/armstub7.S#L135 [3] https://github.com/raspberrypi/tools/blob/49719d554/armstubs/armstub7.S#L64 [4] https://gitlab.denx.de/u-boot/u-boot/blob/v2015.04/include/configs/rpi-common.h#L18 [5] https://github.com/raspberrypi/linux/commit/d9fac63adac#diff-6722037d79570df5b392a49e0e006573R526 [6] http://lists.infradead.org/pipermail/linux-rpi-kernel/2015-February/001268.html
Cc: Zoltán Baldaszti <address@hidden>
Cc: Pekka Enberg <address@hidden>
Cc: Stephen Warren <address@hidden>
Cc: Kshitij Soni <address@hidden>
Cc: Michael Chan <address@hidden>
Cc: Andrew Baumann <address@hidden>
Reviewed-by: Alistair Francis <address@hidden>
Signed-off-by: Philippe Mathieu-Daudé <address@hidden>
hw/arm/raspi.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/hw/arm/raspi.c b/hw/arm/raspi.c
index 3996f6c63a..ef76a27f33 100644
--- a/hw/arm/raspi.c
+++ b/hw/arm/raspi.c
@@ -29,8 +29,7 @@
#define FIRMWARE_ADDR_3 0x80000 /* Pi 3 loads kernel.img here by default */
#define SPINTABLE_ADDR  0xd8 /* Pi 3 bootloader spintable */

-/* Table of Linux board IDs for different Pi versions */
-static const int raspi_boardid[] = {[1] = 0xc42, [2] = 0xc43, [3] = 0xc44};

Maybe worth a comment about why using this number (short, one line version of commit message).

You mean something like:

/* Registered machine type:
* https://www.arm.linux.org.uk/developer/machines/list.php?mid=3138

I think a link in a comment is not very convenient (and may break if the website is ever moved) so maybe just a line to say why this particular number was chosen would be better, such as

/* This matches RPi Foundation bootloader and U-Boot */

+#define MACH_TYPE_BCM2708   3138 /* Linux board IDs */

The rest of the detailed explanation could be looked up in the commit message. Just suggested the comment to warn readers that this is not a mistake but a pecularity of the platform.


reply via email to

[Prev in Thread] Current Thread [Next in Thread]