[PATCH] ARM: /proc/cpuinfo: Use DT machine name when possible

On Wed, Jun 18, 2014 at 2:22 PM, Pali Roh?r [off-list ref] wrote:

On Wednesday 18 June 2014 21:07:35 Rob Herring wrote:

quoted

On Wed, Jun 18, 2014 at 11:54 AM, Pali Roh?r

[off-list ref] wrote:

quoted

quoted

Machine name from board description is some generic name on
DT kernel. DT provides machine name property which is
specific for board, so use it instead generic one when
possible.

Signed-off-by: Pali Roh?r <redacted>
---

 arch/arm/kernel/setup.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/arm/kernel/setup.c

b/arch/arm/kernel/setup.c index 8a16ee5..fbc7b4f 100644

--- a/arch/arm/kernel/setup.c
+++ b/arch/arm/kernel/setup.c

@@ -875,10 +875,13 @@ void __init setup_arch(char

**cmdline_p)

        setup_processor();
        mdesc = setup_machine_fdt(__atags_pointer);

-       if (!mdesc)
+       if (mdesc)
+               machine_name =
of_flat_dt_get_machine_name(); +       else

                mdesc = setup_machine_tags(__atags_pointer,
                __machine_arch_type);

        machine_desc = mdesc;

-       machine_name = mdesc->name;
+       if (!machine_name)
+               machine_name = mdesc->name;

        if (mdesc->reboot_mode != REBOOT_HARD)

                reboot_mode = mdesc->reboot_mode;

I did a similar patch previously[1]. Like my original patch,
your patch unconditionally changes the name which could be
considered part of the userspace ABI. It's arguably not good
practice for userspace to depend on the name, but there are
likely cases that do. So I think this needs to be optional
and only use the DT name if the machine desc name is NULL.

So something like the below and then change the machine
descriptors you care about. The default generic DT machine
desc should definitely be changed.

I had a follow-up discussion with Grant about his concerns in
the thread about knowing which machine desc used to boot. He
said he was okay if just the machine desc address is printed
out.

diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
index 50e198c..1479250 100644
--- a/arch/arm/kernel/setup.c
+++ b/arch/arm/kernel/setup.c

@@ -887,7 +887,7 @@ void __init setup_arch(char **cmdline_p)
        if (!mdesc)
                mdesc = setup_machine_tags(__atags_pointer,

__machine_arch_type);
        machine_desc = mdesc;
-       machine_name = mdesc->name;
+       machine_name = mdesc->name ? mdesc->name :
of_flat_dt_get_machine_name();

        if (mdesc->reboot_mode != REBOOT_HARD)
                reboot_mode = mdesc->reboot_mode;


[1]
http://lists.infradead.org/pipermail/linux-arm-kernel/2013-No
vember/208878.html

Hi,

now legacy board code for Nokia N900 (RX-51) is migrating to DT
kernel and there is problem with info which /proc/cpuinfo reports

Thanks for providing your motivation which was missing from the commit message.

New DT kernel (3.16-rc1) reports:

# busybox cat /proc/cpuinfo
processor       : 0
model name      : ARMv7 Processor rev 3 (v7l)
Features        : swp half thumb fastmult vfp edsp thumbee neon
vfpv3 tls vfpd32
CPU implementer : 0x41
CPU architecture: 7
CPU variant     : 0x2
CPU part        : 0xc08
CPU revision    : 3

Hardware        : Generic OMAP3 (Flattened Device Tree)
Revision        : 0000
Serial          : 0000000000000000

But legacy board code kernel reports:

# busybox cat /proc/cpuinfo
processor       : 0
model name      : ARMv7 Processor rev 3 (v7l)
Features        : swp half thumb fastmult vfp edsp thumbee neon
vfpv3 tls vfpd32
CPU implementer : 0x41
CPU architecture: 7
CPU variant     : 0x2
CPU part        : 0xc08
CPU revision    : 3

Hardware        : Nokia RX-51 board
Revision        : 0012
Serial          : 0000000000000000

Basically in DT kernel is missing Hardware, Revision and probably
also Serial key. (Now I used only qemu for testing which set
serial key to 0). All these informations is used by userspace
applications which determinate how to behave.

It is somewhat fragile to expect the name in the DT to match the old
name from the kernel. As your patch to n900 dts shows, we'd probably
have to update every dts file to make them match. While I think we
should work to remove this string from the kernel, userspace depending
on the DT model string is a bad idea. For example, if you had some
platform with multiple OEMs just rebranding the same base design, they
may all want to put their own model string into each product. The true
h/w id is the compatible string.

Serial number is easy. There is already a standard although not widely
used property for it with "/serial-number". You just need to wire it
up to cpuinfo.

So without this patch DT migration for Nokia N900 cannot be done
without breaking userspace - which is not acceptable...

I agree, but I would like to come up with something that prevents
future dependence on this string.

Also I still did not know why DT kernel does not report Revision
number which is passed by bootloader via atags. Any idea?

Probably because no one cared until now and revision info for every
SOC is different. I would like to see revision info set in the DT in a
standard way and remove the various SOC specific kernel
implementations.

Rob