From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ian Campbell <Ian.Campbell@citrix.com>
Subject: Re: [PATCH ARM v8 2/4] mini-os: arm: interrupt
 controller
Date: Tue, 21 Oct 2014 16:35:22 +0100
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To: Julien Grall <julien.grall@linaro.org>
Cc: Thomas Leonard <talex5@gmail.com>, Dave.Scott@eu.citrix.com, stefano.stabellini@eu.citrix.com, anil@recoil.org, samuel.thibault@ens-lyon.org, xen-devel@lists.xenproject.org
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On Tue, 2014-10-21 at 16:22 +0100, Julien Grall wrote:
> On 10/21/2014 04:16 PM, Ian Campbell wrote:
> > On Tue, 2014-10-21 at 15:26 +0100, Julien Grall wrote:
> >> Our implementation of ITARGETSR doesn't handle correctly read/write per
> >> byte. If the register is RO (such as for the SGIs and PPIs), our write
> >> ignore is checking that the guest is writing a word.
> > 
> > That's a bug.
> 
> Agree
> 
> >> Even though we need to fix it in Xen (I could send a patch for it). We
> >> need to keep this implementation if we want mini-os to run on Xen 4.4.x.
> > 
> > We should fix bugs, not workaround them in the guest.
> 
> Writing a 32 bits value into those registers is perfectly value and not
> a workaround.

If you would normally write 1 byte (which makes perfect sense for this
register) but can't because of a Xen bug then avoiding that by
read/modify/write of 4 bytes because of a Xen bug *is* a workaround.

> In this case, it would make mini-os working directly on Xen 4.4.

and how long should mini-os carry this hack for then?

Ian.