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SubjectRe: [v4 PATCH 8/8] RISC-V: Assign hwcap as per comman capabilities.
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On 2/13/19 12:44 AM, Johan Hovold wrote:
> On Tue, Feb 12, 2019 at 11:58:10AM -0800, Atish Patra wrote:
>> 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@wdc.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 ?
>
> The problem is that the proposed code might still set elf_hwcap -- it
> all depends on the order of the hart nodes in dt (i.e. it will only be
> left unset if the first node is malformed).
>
> For that reason, I'd say it's better to either bail out (hard or at
> least with elf_hwcap unset) or to continue processing the other nodes.
>
> The former might break current systems with malformed dt, though.
>
> And since the harts are expected to have the same ISA, continuing the
> processing while warning and ignoring the malformed node might be
> acceptable.
>

ok. I will change it to continue unless somebody else has objection.

Thanks for the review.

Regards,
Atish
> Johan
>

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