Re: [PATCH 01/15] hw/intc/armv7m_nvic: Make all of system PPB range be RAZWI/BusFault

From: Richard Henderson <richard.henderson@linaro.org>
To: Peter Maydell <peter.maydell@linaro.org>,
	qemu-arm@nongnu.org, qemu-devel@nongnu.org
Subject: Re: [PATCH 01/15] hw/intc/armv7m_nvic: Make all of system PPB range be RAZWI/BusFault
Date: Tue, 17 Nov 2020 11:07:19 -0800	[thread overview]
Message-ID: <c3b2e0dd-0a7f-3c9c-1e14-d358ea15f1f7@linaro.org> (raw)
In-Reply-To: <20201116160831.31000-2-peter.maydell@linaro.org>

On 11/16/20 8:08 AM, Peter Maydell wrote:
> For M-profile CPUs, the range from 0xe0000000 to 0xe00fffff is the
> Private Peripheral Bus range, which includes all of the memory mapped
> devices and registers that are part of the CPU itself, including the
> NVIC, systick timer, and debug and trace components like the Data
> Watchpoint and Trace unit (DWT).  Within this large region, the range
> 0xe000e000 to 0xe000efff is the System Control Space (NVIC, system
> registers, systick) and 0xe002e000 to 0exe002efff is its Non-secure
> alias.
> 
> The architecture is clear that within the SCS unimplemented registers
> should be RES0 for privileged accesses and generate BusFault for
> unprivileged accesses, and we currently implement this.
> 
> It is less clear about how to handle accesses to unimplemented
> regions of the wider PPB.  Unprivileged accesses should definitely
> cause BusFaults (R_DQQS), but the behaviour of privileged accesses is
> not given as a general rule.  However, the register definitions of
> individual registers for components like the DWT all state that they
> are RES0 if the relevant component is not implemented, so the
> simplest way to provide that is to provide RAZ/WI for the whole range
> for privileged accesses.  (The v7M Arm ARM does say that reserved
> registers should be UNK/SBZP.)
> 
> Expand the container MemoryRegion that the NVIC exposes so that
> it covers the whole PPB space. This means:
>  * moving the address that the ARMV7M device maps it to down by
>    0xe000 bytes
>  * moving the off and the offsets within the container of all the
>    subregions forward by 0xe000 bytes
>  * adding a new default MemoryRegion that covers the whole container
>    at a lower priority than anything else and which provides the
>    RAZWI/BusFault behaviour
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

r~