Date:	Tue, 20 Jan 2015 20:17:52 +0800
From:	Hanjun Guo <hanjun.guo@...aro.org>
To:	Mark Rutland <mark.rutland@....com>
CC:	Catalin Marinas <Catalin.Marinas@....com>,
	"jcm@...hat.com" <jcm@...hat.com>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	"linaro-acpi@...ts.linaro.org" <linaro-acpi@...ts.linaro.org>,
	Will Deacon <Will.Deacon@....com>,
	"wangyijing@...wei.com" <wangyijing@...wei.com>,
	Rob Herring <robh@...nel.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Al Stone <al.stone@...aro.org>,
	Timur Tabi <timur@...eaurora.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	Charles Garcia-Tobin <Charles.Garcia-Tobin@....com>,
	"phoenix.liyi@...wei.com" <phoenix.liyi@...wei.com>,
	Robert Richter <rric@...nel.org>,
	Jason Cooper <jason@...edaemon.net>,
	Arnd Bergmann <arnd@...db.de>,
	Marc Zyngier <Marc.Zyngier@....com>,
	Mark Brown <broonie@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"graeme.gregory@...aro.org" <graeme.gregory@...aro.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
	Sudeep Holla <Sudeep.Holla@....com>,
	Olof Johansson <olof@...om.net>, leif.lindholm@...aro.org
Subject: Re: [PATCH v7 04/17] ARM64 / ACPI: Introduce early_param for "acpi"
 and pass acpi=force to enable ACPI

On 2015年01月20日 19:10, Mark Rutland wrote:
> On Tue, Jan 20, 2015 at 09:29:14AM +0000, Hanjun Guo wrote:
>> On 2015年01月20日 02:01, Mark Rutland wrote:
>>> On Mon, Jan 19, 2015 at 05:52:33PM +0000, Catalin Marinas wrote:
>>>> On Mon, Jan 19, 2015 at 04:59:47PM +0000, Jon Masters wrote:
>>>>> On 01/19/2015 10:13 AM, Grant Likely wrote:
>>>>>> On Mon, 19 Jan 2015 13:51:45 +0000
>>>>>> , Catalin Marinas <catalin.marinas@....com>
>>>>>>    wrote:
>>>>>>> On Mon, Jan 19, 2015 at 11:55:32AM +0000, Ard Biesheuvel wrote:
>>>>>>>> On 19 January 2015 at 11:42, Catalin Marinas <catalin.marinas@....com> wrote:
>>>>>>>>> On Wed, Jan 14, 2015 at 03:04:52PM +0000, Hanjun Guo wrote:
>>>>>>>>>> From: Al Stone <al.stone@...aro.org>
>>>>>>>>>>
>>>>>>>>>> Introduce one early parameters "off" and "force" for "acpi", acpi=off
>>>>>>>>>> will be the default behavior for ARM64, so introduce acpi=force to
>>>>>>>>>> enable ACPI on ARM64.
>>>>>>>>>>
>>>>>>>>>> Disable ACPI before early parameters parsed, and enable it to pass
>>>>>>>>>> "acpi=force" if people want use ACPI on ARM64. This ensures DT be
>>>>>>>>>> the prefer one if ACPI table and DT both are provided at this moment.
>>>>>>>>> [...]
>>>>>>>>>> --- a/arch/arm64/kernel/setup.c
>>>>>>>>>> +++ b/arch/arm64/kernel/setup.c
>>>>>>>>>> @@ -62,6 +62,7 @@
>>>>>>>>>>    #include <asm/memblock.h>
>>>>>>>>>>    #include <asm/psci.h>
>>>>>>>>>>    #include <asm/efi.h>
>>>>>>>>>> +#include <asm/acpi.h>
>>>>>>>>>>
>>>>>>>>>>    unsigned int processor_id;
>>>>>>>>>>    EXPORT_SYMBOL(processor_id);
>>>>>>>>>> @@ -388,6 +389,8 @@ void __init setup_arch(char **cmdline_p)
>>>>>>>>>>         early_fixmap_init();
>>>>>>>>>>         early_ioremap_init();
>>>>>>>>>>
>>>>>>>>>> +     disable_acpi();
>>>>>>>>>> +
>>>>>>>>>>         parse_early_param();
>>>>>>>>>>
>>>>>>>>>>         /*
>>>>>>>>>
>>>>>>>>> Did we get to any conclusion here? DT being the preferred one is fine
>>>>>>>>> when both DT and ACPI are present but do we still want the kernel to
>>>>>>>>> ignore ACPI altogether if DT is not present? It's a bit harder to detect
>>>>>>>>> the presence of DT at this point since the EFI_STUB added one already. I
>>>>>>>>> guess we could move the "acpi=force" argument passing to EFI_STUB if no
>>>>>>>>> DT is present at boot.
>>>>>>>>
>>>>>>>> Since the EFI stub populates the /chosen node in DT, I would prefer
>>>>>>>> for it to add a property there to indicate whether it created the DT
>>>>>>>> from scratch rather than adding ACPI specific stuff in there (even if
>>>>>>>> it is just a string to concatenate)
>>>>>>>
>>>>>>> This works for me. So we could pass "acpi=force" in EFI stub if it
>>>>>>> created the DT from scratch *and* ACPI tables are present (can it detect
>>>>>>> the latter? And maybe it could print something if none are available).
>>>>>>> If that works, the actual kernel can assume that ACPI needs to be
>>>>>>> explicitly enabled via acpi=force, irrespective of how much information
>>>>>>> it has in DT.
>>>>>>
>>>>>> Ditto for me. I think this is a fine solution. And, yes, the stub can
>>>>>> easily detect the presence of ACPI by looking in the UEFI config table.
>>>>>
>>>>> I get the point behind doing this, but could we not have it pass in a
>>>>> different parameter than =force? Perhaps something new? I'd like to
>>>>> separate out the case that it was enabled automatically vs explicitly
>>>>> forced on by a user wanting to use ACPI on a system with both tables.
>>>>
>>>> Ard had a point, so we should probably not pass acpi=force from EFI stub
>>>> (especially since a user may explicitly pass acpi=off irrespective of DT
>>>> presence). Some other property in the chosen node? It's not even an ABI
>>>> since that's a contract between EFI stub and the rest of the kernel, so
>>>> an in-kernel only interface.
>>>
>>> Not strictly true once kexec is in place. Then it becomes a stub ->
>>> kernel -> kernel -> kernel -> ... interface, alnog with the rest of the
>>> properties the stub puts in the DTB.
>>>
>>> Having something like /chosen/linux,uefi-stub-generated-dtb sounds sane
>>> regardless.
>>
>> How about the patch (just RFC, maybe it is horrible :) ) below:
>>
>> When system supporting both DT and ACPI but firmware providing
>> no dtb, we can use this linux,uefi-stub-generated-dtb property
>> to let kernel know that we can try ACPI configuration data.
>>
>> Signed-off-by: Hanjun Guo <hanjun.guo@...aro.org>
>> ---
>>    Documentation/devicetree/bindings/chosen.txt | 19 ++++++++++++++++
>>    arch/arm64/kernel/setup.c                    | 34
>> +++++++++++++++++++++++++++-
>>    drivers/firmware/efi/libstub/fdt.c           |  6 +++++
>>    3 files changed, 58 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/devicetree/bindings/chosen.txt
>> b/Documentation/devicetree/bindings/chosen.txt
>> index ed838f4..18776b9 100644
>> --- a/Documentation/devicetree/bindings/chosen.txt
>> +++ b/Documentation/devicetree/bindings/chosen.txt
>> @@ -44,3 +44,22 @@ Implementation note: Linux will look for the property
>> "linux,stdout-path" or
>>    on PowerPC "stdout" if "stdout-path" is not found.  However, the
>>    "linux,stdout-path" and "stdout" properties are deprecated. New platforms
>>    should only use the "stdout-path" property.
>> +
>> +
>> +linux,uefi-stub-generated-dtb property
>> +--------------------------------------
>> +
>> +UEFI stub will generate this property in the chosen node to let linux
>> kernel
>> +know that there is no DTB provided by firmware.
>> +
>> +There is a use case for system supporting both DT and ACPI, when firmware
>> +doesn't provide DT, we can try ACPI configration data to boot the system.
>
> I don't think we need to list potential use cases here, this can be
> useful regardless of UEFI.

OK.

>
> The other UEFI stub properties currently live under
> Documentation/arm/uefi.txt. This should live with them.

OK, will update in next version.

>
>> +
>> +Usage:
>> +
>> +linux,uefi-stub-generated-dtb = "true" means that it is true that the dtb
>> +is generated by uefi stub
>> +
>> +or
>> +
>> +linux,uefi-stub-generated-dtb = "false" is the reverse.
>
> I imagined this would be an empty property. It would only be present if
> the stub generated the DTB, and has no value:
>
> /chosen {
> 	linux,uefi-stub-generated-dtb;
> };
>
>> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
>> index 54e39e3..8268c7b 100644
>> --- a/arch/arm64/kernel/setup.c
>> +++ b/arch/arm64/kernel/setup.c
>> @@ -371,6 +371,31 @@ static void __init request_standard_resources(void)
>>    	}
>>    }
>>
>> +int __init dt_scan_chosen(unsigned long node, const char *uname,
>> +			int depth, void *data)
>> +{
>> +	const char *p;
>> +	
>> +	if (depth != 1 || !data ||
>> +	    (strcmp(uname, "chosen") != 0 && strcmp(uname, "chosen@0") != 0))
>> +		return 0;
>
> Do we ever generate chosen@0, and do we even accept that?

Sorry, I have limited knowledge about the history of DT, so I think you
meant that I just need to check strcmp(uname, "chosen") here, right?

>
>> +
>> +	p = of_get_flat_dt_prop(node, "linux,uefi-stub-generated-dtb", NULL);
>> +	if (!p && !strcmp(p, "true"))
>> +		*data = true;
>> +
>> +	return 1;
>> +}
>> +
>> +static bool __init is_uefi_stub_generated_dtb(void)
>> +{
>> +	bool flag = false;
>> +
>> +	of_scan_flat_dt(dt_scan_chosen, &flag);
>> +
>> +	return flag;
>> +}
>> +
>>    u64 __cpu_logical_map[NR_CPUS] = { [0 ... NR_CPUS-1] = INVALID_HWID };
>>
>>    void __init setup_arch(char **cmdline_p)
>> @@ -389,7 +414,14 @@ void __init setup_arch(char **cmdline_p)
>>    	early_fixmap_init();
>>    	early_ioremap_init();
>>
>> -	disable_acpi();
>> +	/*
>> +	 * If no dtb provided by firmware, enable ACPI
>> +	 * and try to boot with ACPI configuration data
>> +	 */
>> +	if (is_uefi_stub_generated_dtb())
>> +		enable_acpi();
>> +	else
>> +		disable_acpi();
>>
>>    	parse_early_param();
>>
>> diff --git a/drivers/firmware/efi/libstub/fdt.c
>> b/drivers/firmware/efi/libstub/fdt.c
>> index c846a96..9e2084b 100644
>> --- a/drivers/firmware/efi/libstub/fdt.c
>> +++ b/drivers/firmware/efi/libstub/fdt.c
>> @@ -154,6 +154,12 @@ efi_status_t update_fdt(efi_system_table_t
>> *sys_table, void *orig_fdt,
>>    	if (status)
>>    		goto fdt_set_fail;
>>
>> +	/* Add a property to show the dtb is generated by uefi stub or not */
>> +	status = fdt_setprop_string(fdt, node, "linux,uefi-stub-generated-dtb",
>> +				orig_fdt ? "false" : "true");
>> +	if (status)
>> +		goto fdt_set_fail;
>> +
>
> This should create an empty property, and only when generated by the
> stub.

OK. could you give me some guidance to use which API to create an
empty property? I try to find but failed.

Thanks for the review!

Hanjun
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