Re: [Xen-devel] [PATCH v6 09/31] xen/arm: ITS: Add APIs to add and assign device

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 09/09/15 16:07, Ian Campbell wrote:
>> In the ITS, discard means removing the mapping from the MSI (eventID) to
>> the LPI.
> 
> Table 6-6 in the gic arch spec (ARM IHI 0069A (ID060315)) says about the
> discard ITS command "Translates the event defined by EventID and DeviceID
> and instructs the appropriate Redistributor to remove the pending state of
> the interrupt. It also ensures that any caching in the Redistributors
> associated with a specific EventID is consistent with the configuration
> held in memory."
> 
> And section 6.3.4 seems to agree _except_ for the pseudo code which does
> indeed seem to include setting the corresponding ITE entry to invalid.
> 
> Given that the pseudocode for CLEAR appears to match how DISCARD is
> decribed (infact the descrpitions of CLEAR and DISCARD look functionally
> identical to me) I'm inclined to believe the pseudo code for DISCARD, i.e.
> the docs are misleading and you are correct that DISCARD is more than just
> clearing the pending state.
> 
> The older PRD03-GENC-010745 24.0 looks to be more correct.
> 
> So sorry for the noise, that'll teach me to believe docs.

Actually, I didn't read the newer spec but remembered from what I read
on the PRD03-* one.

After reading the newer spec, the description doesn't match the
pseudo-code. Might be worth to ask ARM about to clarify the behavior?

Regards,

-- 
Julien Grall

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