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Re: [PATCH for-6.2 0/2] escc: fixes for STATUS_TXEMPTY and SPEC_ALLSENT

From: Mark Cave-Ayland
Subject: Re: [PATCH for-6.2 0/2] escc: fixes for STATUS_TXEMPTY and SPEC_ALLSENT
Date: Sun, 21 Nov 2021 09:40:41 +0000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.14.0

On 18/11/2021 18:23, Peter Maydell wrote:

On Thu, 18 Nov 2021 at 18:18, Mark Cave-Ayland
<mark.cave-ayland@ilande.co.uk> wrote:

This is another attempt to fix booting 32-bit QEMU SPARC machines in
qemu-system-sparc using a real Sun PROM based upon further experiments and
re-reading of the ESCC datasheet from a previous patch posted at

It appears that both the Sun PROM and OpenBSD with OpenBIOS fail to send an
explicit reset command as recommended in the ESCC datasheet, which causes
hangs during serial port enumeration since the introduction of the recent
ESCC reset changes.

The first patch always sets STATUS_TXEMPTY in R_STATUS on hardware reset
which wasn't documented in the "Reset" section(s) but is documented in the
"Transmit Interrupts and Transmit Buffer Empty Bit" section, whilst the
second patch updates SPEC_ALLSENT when writing to W_TXCTRL1.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>

Thanks Peter. I've added this to my qemu-sparc queue and will send a PR shortly with both yours and Philippe's R-B tags.



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