Hi Simon,
2015-12-31 13:08 GMT+08:00 Simon Glass <s...@chromium.org>:
> Hi Maio,
>
> On 30 December 2015 at 19:55, Miao Yan <yanmiaob...@gmail.com> wrote:
>> Add a function to fix up 'cpus' node in dts files for qemu target.
>>
>> Signed-off-by: Miao Yan <yanmiaob...@gmail.com>
>> ---
>> Changes in v4:
>> - fix a typo in commit log
>>
>> arch/x86/cpu/qemu/fw_cfg.c | 65
>> ++++++++++++++++++++++++++++++++++++++++++++++
>> arch/x86/cpu/qemu/fw_cfg.h | 11 ++++++++
>> 2 files changed, 76 insertions(+)
>
> I'm sorry for not reviewing this earlier (Christmas and all that). I
> don't think you need to update the device tree to make this work.
>
> Here's my suggestion:
I am not familiar with driver model so I am not sure if I understand
you correctly. Are you suggesting something like the following:
+
+void create_cpu_node(void)
+{
+ int ret;
+ int cpu_online;
+ int cpu_num = 0;
+ struct udevice *dev;
+ struct cpu_platdata *plat;
+
+ for (uclass_find_first_device(UCLASS_CPU, &dev);
+ dev;
+ uclass_find_next_device(&dev)) {
+ cpu_num++;
+ }
+
+ cpu_online = qemu_fwcfg_online_cpus();
+ printf("%d cpus probed, %d cpus online\n", cpu_num, cpu_online);
+
+ for (dev = NULL; cpu_num < cpu_online; cpu_num++) {
+ ret = device_bind_driver(cpus_dev, "cpu_qemu", "cpu", &dev);
+ if (ret < 0) {
+ printf("device_bind_driver failed with code %d\n", ret);
+ return;
+ }
+ plat = dev_get_parent_platdata(dev);
+ plat->cpu_id = cpu_num;
+ }
+}
>
> - At present cpu_x86_bind() sets up the CPU APIC ID from the device tree
> - You can bind new CPU devices in your code on start-up
> - You can check if you have CPUs which are not available in the device
> list, by using uclass_find_first/next_device() to iterate through the
> devices without probing them
> - Then to create a new one, call device_bind_driver() with the /cpus
> node as the parent
The 'cpus' node is created in uclass_cpu_init(), and all the
'cpu' subnode are created by scanning device tree. But arch_early_init_r()
is called before uclass_cpu_init(), so at that time, there's no
'cpus' yet.
Seems we need somewhere after uclass_cpu_init() but before mp_init() ?
Or we entirely bypass the cpu uclass driver and create /cpus too ?
> - After binding, update the parent platform data:
>
> struct cpu_platdata *plat = dev_get_parent_platdata(dev);
>
> plat->cpu_id = ...
>
> - Then when it comes to probing, you will have all the devices you
> need, and you don't need to adjust the device tree. The device tree
> can just hold a single device, for example.
>
> I think it is better to do this than adjust the device tree because it
> removes the 32-CPU limit and should be faster. It is also simpler as
> it is a more direct method. Also I believe you only need to do this
> after relocation - e.g. in arch_early_init_r(), which is before
> mp_init() is called from cpu_init_r().
Seems I can't do it in arch_early_init_r(), when 'cpus' is available yet.
>
> I wonder if there is a general way to probe available CPUs (and their
> APIC IDs)? Or is qemu the only 'CPU' with this feature?
I am not sure about other x86 boards, but certainly fw_cfg is
not the generic way. Maybe Bin can comment on this.
>
> Regards,
> Simon
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