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Re: [PATCH for-6.2 2/2] escc: update the R_SPEC register SPEC_ALLSENT bi
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From: |
Philippe Mathieu-Daudé |
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Subject: |
Re: [PATCH for-6.2 2/2] escc: update the R_SPEC register SPEC_ALLSENT bit when writing to W_TXCTRL1 |
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Date: |
Thu, 18 Nov 2021 19:26:15 +0100 |
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User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.0 |
On 11/18/21 19:18, Mark Cave-Ayland wrote:
> The ESCC datasheet states that SPEC_ALLSENT is always set in sync mode and set
> in async mode once all characters have cleared the transmitter. Since writes
> to
> SERIAL_DATA use a synchronous chardev API, the guest can never see the state
> when
> transmission is in progress so it is possible to set SPEC_ALLSENT in the
> R_SPEC register unconditionally.
>
> This fixes a hang when using the Sun PROM as it attempts to enumerate the
> onboard serial devices, and a similar hang in OpenBSD SPARC32 where in both
> cases
> the boot process will not proceed until SPEC_ALLSENT has been set after
> writing
> to W_TXCTRL1.
>
> Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
> ---
> hw/char/escc.c | 14 ++++++++++++++
> 1 file changed, 14 insertions(+)
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>