Re: [RFC PATCH 0/2] hw/char/bcm2835_aux: Provide full 16550 UART support

[Philippe Mathieu-Daudé]

Hi Peter,

On 9/23/19 3:26 PM, Peter Maydell wrote:
> On Tue, 20 Aug 2019 at 13:34, Philippe Mathieu-Daudé <address@hidden> wrote:
>> Since there has been some activity on the list asking about
>> Rasberry PI USB support, I had a look a some previous unfinished
>> work and rebased it to share, in case it helps hobbyist interested
>> in improving these machines.
>>
>> This series is some proof-of-concept on improving the AUX UART
>> support. See the commit description for various TODO/questions.
> 
> Apologies for not having got round to looking at this
> RFC patchset sooner...

No worry, this patch is not very important.

> I think my question here would be -- is using the 16650 emulation
> really the right thing? The BCM2835 documentation says
> "The implemented UART is *not* a 16650 compatible UART. However
> as far as possible the first 8 control and status registers are
> laid out *like* a 16550 UART." That suggests to me that it would
> be better to just improve our model of this hardware rather than
> to replace it with a 16550 model which isn't what the hardware
> really is.

Some registers are the same as the 16550, some others only implement
bits (identically placed). None provide extra bit (a new bit not present
in the 16550, for that they used new registers).

My idea was to reduce/reuse the chardev code.
I think a correct way is using the "hw/register.h" API to mask the
unimplemented bits.

This patch reduces a lot of [LCR/LSR/MCR/MSR] "register unimplemented"
when booting Linux, but from the emulation point of view they are
harmless, so we can ignore this patch for now.

Thanks,

Phil.