Subject: Re: [PATCH v2 01/10] mailbox: Support blocking transfers in atomic context

From: Greg KH <[email-masked]>
Date: Fri, 7 Dec 2018 16:39:01 +0100

On Fri, Dec 07, 2018 at 12:32:45PM +0100, Thierry Reding wrote:
> Greg,
> 
> any ideas on how we can move forward here? For reasons given elsewhere
> in this thread I understand that there is no way to make the console
> code run in non-atomic context. Have you ever run into a case where the
> console driver couldn't busy-loop? Were there any solutions to this?

I don't know of any such cases, hardware sucks at times, and we just
have to deal with getting it to work by doing stuff like this :(

> I've looked through quite a few drivers and they all end up with a busy
> loop, waiting for the transmission FIFO to become empty. There are also
> a few implementations for hypervisors that call back into some firmware
> in order to send the characters, but I expect those to do the busy
> looping in the firmware.

busy loops are ok here, as you point out.

> Perhaps the most prominent case that I came across and that is quite
> similar to this discussion is netconsole. There's a lot of code in the
> network layer that exists only to allow using a network device for
> outputting a console. I don't think the changes to the mailbox
> framework are anywhere near as complicated.

Neither do I, I have no objection to your changes at all.

thanks,

greg k-h

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