On 28/09/2016 15:10, Thomas Huth wrote:
> On 28.09.2016 14:41, Laurent Vivier wrote:
>>
>>
>> On 28/09/2016 14:23, Thomas Huth wrote:
>>> On 28.09.2016 14:13, Laurent Vivier wrote:
>>>>
>>>>
>>>> On 28/09/2016 12:18, Thomas Huth wrote:
>>>>> Transactional memory is currently only supported on KVM-HV, and
>>>>> not yet on KVM-PR. So it's better to check the device tree first
>>>>> and fail gracefully if it's not available.
>>>>>
>>>>> Signed-off-by: Thomas Huth <thuth@xxxxxxxxxx>
>>>>> ---
>>>>> powerpc/tm.c | 31 +++++++++++++++++++++++++++++++
>>>>> 1 file changed, 31 insertions(+)
>>>>>
>>>>> diff --git a/powerpc/tm.c b/powerpc/tm.c
>>>>> index 6ce750a..83d9d3d 100644
>>>>> --- a/powerpc/tm.c
>>>>> +++ b/powerpc/tm.c
>>>>> @@ -10,6 +10,32 @@
>>>>> #include <asm/processor.h>
>>>>> #include <asm/handlers.h>
>>>>> #include <asm/smp.h>
>>>>> +#include <asm/setup.h>
>>>>> +#include <devicetree.h>
>>>>> +
>>>>> +/* Check "ibm,pa-features" property of a CPU node for the TM flag */
>>>>> +static void cpu_has_tm(int fdtnode, u32 regval __unused, void *ptr)
>>>>> +{
>>>>> + const struct fdt_property *prop;
>>>>> + int plen;
>>>>> +
>>>>> + prop = fdt_get_property(dt_fdt(), fdtnode, "ibm,pa-features", &plen);
>>>>> + assert(prop != NULL);
>>>>> +
>>>>> + if (plen >= 26 && prop->data[1] == 0 && (prop->data[24] & 0x80) != 0)
>>>>> + *(int *)ptr += 1;
>>>>
>>>> Perhaps some comments can help here:
>>>> why do you check plen >= 26 and not >= 25?
>>>> why do you check prop->data[1]?
>>>
>>> Well, it's all in the (Lo-)PAPR spec, but I can add a comment there if
>>> you like.
>>
>> Well, even with the spec, it's not really clear.
>>
>>>> why don't you check prop->data[23] for the size of the attribute?
>>>
>>> I guess you mean prop->data[0] ? ... sure, I can add that check, too.
>>
>> No in fact, I didn't understand correctly the spec. :)
>>
>> So date[0] is the size, should be plen (so no need to add the check)
>> date[1] is the type, should be "0" ("attribute-specifier-type", you
>> check it)
>> and then an array( "attribute-specifier"), where byte 22 and 23 are
>> "Level of Transactional Memory Category Support". It's not clear if TM
>> bit is in byte 22 (data[24]) or in byte 23 (data[25]). How do you know?
>
> That's the way how it is encoded in QEMU currently, and the byte the
> Linux kernel looks at. So I think it's right.
thanks, I think it could be good to have a comment.
Reviewed-by: Laurent Vivier <lvivier@xxxxxxxxxx>
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
