[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [PATCH for-6.2 2/2] escc: update the R_SPEC register SPEC_ALLSENT bi

From: Philippe Mathieu-Daudé
Subject: Re: [PATCH for-6.2 2/2] escc: update the R_SPEC register SPEC_ALLSENT bit when writing to W_TXCTRL1
Date: Thu, 18 Nov 2021 19:26:15 +0100
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>

reply via email to

[Prev in Thread] Current Thread [Next in Thread]