linux-kernel - Re: [v4 PATCH 8/8] RISC-V: Assign hwcap as per comman capabilities.

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Message-ID: <61766631-42f4-ec25-3b5c-ae892da44ccb@wdc.com>
Date:   Tue, 12 Feb 2019 11:58:10 -0800
From:   Atish Patra <atish.patra@....com>
To:     Johan Hovold <johan@...nel.org>
Cc:     "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        Alan Kao <alankao@...estech.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Andreas Schwab <schwab@...e.de>,
        Anup Patel <anup@...infault.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Dmitriy Cherkasov <dmitriy@...-tech.org>,
        Jason Cooper <jason@...edaemon.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Marc Zyngier <marc.zyngier@....com>,
        Palmer Dabbelt <palmer@...ive.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Rob Herring <robh@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [v4 PATCH 8/8] RISC-V: Assign hwcap as per comman capabilities.

On 2/12/19 3:25 AM, Johan Hovold wrote:
> On Tue, Feb 12, 2019 at 03:10:12AM -0800, Atish Patra wrote:
>> Currently, we set hwcap based on first valid hart from DT. This may not
>> be correct always as that hart might not be current booting cpu or may
>> have a different capability.
>>
>> Set hwcap as the capabilities supported by all possible harts with "okay"
>> status.
>>
>> Signed-off-by: Atish Patra <atish.patra@....com>
>> ---
>>   arch/riscv/kernel/cpufeature.c | 41 ++++++++++++++++++++++-------------------
>>   1 file changed, 22 insertions(+), 19 deletions(-)
>>
>> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
>> index e7a4701f..a1e4fb34 100644
>> --- a/arch/riscv/kernel/cpufeature.c
>> +++ b/arch/riscv/kernel/cpufeature.c
>> @@ -20,6 +20,7 @@
>>   #include <linux/of.h>
>>   #include <asm/processor.h>
>>   #include <asm/hwcap.h>
>> +#include <asm/smp.h>
>>   
>>   unsigned long elf_hwcap __read_mostly;
>>   #ifdef CONFIG_FPU
>> @@ -42,28 +43,30 @@ void riscv_fill_hwcap(void)
>>   
>>   	elf_hwcap = 0;
>>   
>> -	/*
>> -	 * We don't support running Linux on hertergenous ISA systems.  For
>> -	 * now, we just check the ISA of the first "okay" processor.
>> -	 */
>>   	for_each_of_cpu_node(node) {
>> -		if (riscv_of_processor_hartid(node) >= 0)
>> -			break;
>> -	}
>> -	if (!node) {
>> -		pr_warn("Unable to find \"cpu\" devicetree entry\n");
>> -		return;
>> -	}
>> +		unsigned long this_hwcap = 0;
>>   
>> -	if (of_property_read_string(node, "riscv,isa", &isa)) {
>> -		pr_warn("Unable to find \"riscv,isa\" devicetree entry\n");
>> -		of_node_put(node);
>> -		return;
>> -	}
>> -	of_node_put(node);
>> +		if (riscv_of_processor_hartid(node) < 0)
>> +			continue;
>>

>> -	for (i = 0; i < strlen(isa); ++i)
>> -		elf_hwcap |= isa2hwcap[(unsigned char)(isa[i])];
>> +		if (of_property_read_string(node, "riscv,isa", &isa)) {
>> +			pr_warn("Unable to find \"riscv,isa\" devicetree entry\n");
>> +			return;
> 
> Did you want "continue" here to continue processing the other harts?
> 

Hmm. If a cpu node doesn't have isa in DT, that means DT is wrong. A 
"continue" here will let user space use other harts just with a warning 
message?

Returning here will not set elf_hwcap which forces the user to fix the 
DT. I am not sure what should be the defined behavior in this case.

Any thoughts ?
> Note that you currently leak the device node when returning.
> 
Ahh yes. I will fix it if we continue to return in the error case.

Regards,
Atish
> Johan
>