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From: Peter Maydell <peter.maydell@linaro.org>
Date: Tue, 31 Jul 2018 18:18:25 +0100
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Subject: Re: [Qemu-devel] [PATCH v3 3/7] hw/arm: make bitbanded IO optional
 on ARM M Profile
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To: Stefan Hajnoczi <stefanha@redhat.com>
Cc: QEMU Developers <qemu-devel@nongnu.org>, =?UTF-8?Q?Steffen_G=C3=B6rtz?= <mail@steffen-goertz.de>, Alistair Francis <alistair@alistair23.me>, Liviu Ionescu <ilg@livius.net>, qemu-arm <qemu-arm@nongnu.org>, Julia Suvorova <jusual@mail.ru>, Subbaraya Sundeep <sundeep.lkml@gmail.com>, Su Hang <suhang16@mails.ucas.ac.cn>, Steffen Gortz <qemu.ml@steffen-goertz.de>, Jim Mussared <jim@groklearning.com>, Joel Stanley <joel@jms.id.au>

On 25 July 2018 at 09:59, Stefan Hajnoczi <stefanha@redhat.com> wrote:
> Some ARM CPUs have bitbanded IO, a memory region that allows convenient
> bit access via 32-bit memory loads/stores.  This eliminates the need for
> read-modify-update instruction sequences.
>
> This patch makes this optional feature a ARMMProfile qdev property,
> allowing boards to choose whether they want bitbanding or not.
>
> Status of boards:
>  * iotkit (Cortex M33), no bitband
>  * mps2 (Cortex M3), bitband
>  * msf2 (Cortex M3), bitband
>  * stellaris (Cortex M3), bitband
>  * stm32f205 (Cortex M3), bitband
>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

This fixes a bug in the MPS2 boards, incidentally, where the
Ethernet controller is inaccessible because it's hidden by
the shouldn't-be-present bitbanding region...

thanks
-- PMM