Re: [Xen-devel] [PATCH OSSTEST v2 18/20] Osstest/Debian: Add "clk_ignore_unused" to default command line

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi,

Somehow I missed this email.

On 30/10/2014 13:33, Ian Campbell wrote:
> create !
> title it arm: domain 0 disables clocks which are in fact being used
> thanks
>
> On Wed, 2014-10-29 at 16:39 +0000, Ian Jackson wrote:
> > Ian Campbell writes ("[PATCH OSSTEST v2 18/20] Osstest/Debian: Add 
> > "clk_ignore_unused" to default command line"):
> > > This stops dom0 from messing with clocks which it should and is required on
> > > some platforms. It's harmless even when not needed.
> > This is pretty odd.  Doesn't this correspond to some kind of bug, in
> > the dom0 kernel perhaps ?
> dom0 is not aware that some clocks are actually in use (e.g. by the
> hypervisor), so the bug is probably in the lack of some interface to
> communicate this from Xen to dom0, or some other mechanism to gate this.
In reality, Xen is only using the clock of the UART. Even though, I 
think this would also happen with platform device passthrough.
For the latter, it would be fairly easy via a PV drivers. But for 
UART... gating the clock could be a nightmare because every platform 
have their own way to enable/disable the clock. Futhermore, the clock 
could be shared with multiple device...
I'm wondering if we could expose the UART to DOM0 without marking as 
disabled. It would avoid DOM0 to mess up the clock while everything 
would be catch via the vuart implementation in Xen.
Regards,

--
Julien Grall

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel