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Re: [Qemu-devel] [PATCH] versatile: Push lsi initialization to the end


From: Jan Kiszka
Subject: Re: [Qemu-devel] [PATCH] versatile: Push lsi initialization to the end
Date: Mon, 08 Oct 2012 17:28:37 +0200
User-agent: Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv:1.8.1.12) Gecko/20080226 SUSE/2.0.0.12-1.1 Thunderbird/2.0.0.12 Mnenhy/0.7.5.666

On 2012-10-08 17:18, Paolo Bonzini wrote:
> Il 08/10/2012 08:52, Jan Kiszka ha scritto:
>> On 2012-10-06 04:13, Peter Maydell wrote:
>>> On 5 October 2012 19:01, Jan Kiszka <address@hidden> wrote:
>>>> I'm not a fan of this either, but the alternatives are way more
>>>> complicated. We either need to rewrite the chardev subsystem,
>>>> specifically how mux'ed devices are registered and how the active one is
>>>> selected. Or we need to avoid flushing "unrelated" BHs for block
>>>> devices. Not sure of those read requests can be postponed.
>>>
>>> Is this a regression? If it is then the obvious answer is to back
>>> out whatever broke it...
>>
>> I'm using this machine for the first time, so I cannot answer this from
>> the top of my head. However, I don't think it can be a regression.
>>
>> Mux chardevs work like this: You create the backend, then you register
>> the frontend with them, one by one. The last one registered is the first
>> one active. It should also receive the open event of chardev. But as
>> that open even is issued via a BH and last frontend, the serial device,
>> arrives after the first BH flushing, things break.
> 
> Does something like this work instead?
> 
> diff --git a/qemu-char.c b/qemu-char.c
> index b082bae..1ed6d49 100644
> --- a/qemu-char.c
> +++ b/qemu-char.c
> @@ -465,6 +465,9 @@ static void
> mux_chr_update_read_handler(CharDriverState *chr)
>      d->focus = d->mux_cnt;
>      d->mux_cnt++;
>      mux_chr_send_event(d, d->focus, CHR_EVENT_MUX_IN);
> +    if (chr->opened) {
> +        mux_chr_send_event(d, d->focus, CHR_EVENT_OPENED);
> +    }

It's not (only) about a missing event for the serial frontend, it's also
about a spurious open event to the monitor. That generates unwanted
output during startup.

Jan

-- 
Siemens AG, Corporate Technology, CT RTC ITP SDP-DE
Corporate Competence Center Embedded Linux



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