linux-kernel - Re: [PATCH 3/3] serial: 8250: omap: restore registers on shutdown

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Date:	Thu, 06 Aug 2015 15:59:34 +0200
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Peter Hurley <peter@...leysoftware.com>
CC:	John Ogness <john.ogness@...utronix.de>,
	linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Tony Lindgren <tony@...mide.com>, linux-omap@...r.kernel.org,
	nsekhar@...com, nm@...com, linux-serial@...r.kernel.org,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Subject: Re: [PATCH 3/3] serial: 8250: omap: restore registers on shutdown

On 08/06/2015 02:31 PM, Sebastian Andrzej Siewior wrote:

Hi Peter,

>> I'll look at/test this this weekend, ok?
> 
> Sure. I'm currently re-spinning the patches so have everything in
> proper pieces. While at it I will take a look at x_char.

So now that I actually look at it. If I read this right, we never send
the x_char if the TX-DMA never fails to do its job. The comment above
uart_send_xchar() says it is high priority. What do you suggest, wait
until the transfer completes, send the x_char _or_ pause the transfer
send that byte and then send the byte?
In both cases we have to wait until for the FIFO-empty interrupt to
make sure we don't overrun that TX-FIFO.

I *think* waiting until the transfer completes would be simpler but it
is not necessarily high priority.

>> Regards,
>> Peter Hurley

Sebastian
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