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.
Thomas
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