Re: [PATCH v3 3/8] mailbox: Add transmit done by blocking option

From: Mikko Perttunen
Date: Wed Aug 08 2018 - 10:34:23 EST

On 08/08/2018 05:10 PM, Jassi Brar wrote:
On Wed, Aug 8, 2018 at 5:08 PM, Mikko Perttunen <cyndis@xxxxxxxx> wrote:

On 04.08.2018 13:45, Mikko Perttunen wrote:

On 08/03/2018 03:54 PM, Jassi Brar wrote:

On Mon, Jul 2, 2018 at 5:10 PM, Mikko Perttunen <mperttunen@xxxxxxxxxx>

Add a new TXDONE option, TXDONE_BY_BLOCK. With this option, the
send_data function of the mailbox driver is expected to block until
the message has been sent. The new option is used with the Tegra
Combined UART driver to minimize unnecessary overhead when transmitting

1) TXDONE_BY_BLOCK flag :-
Have you tried setting the flag mbox_chan->mbox_client->tx_block

No - I suppose I should have done that. I'm a bit concerned about overhead
as send_data may be called thousands of times per second, so I tried to make
it as close as possible to the downstream driver that just pokes the mailbox
register directly.

I tried using polling in the mailbox framework. Some printing is done from
atomic context so it seems tx_block cannot be used -
wait_for_completion_timeout understandably does not work in atomic context.
I also tried without tx_block, in which case I got some horribly garbled
output, but "Try increasing MBOX_TX_QUEUE_LEN" was readable there.

Any opinions?

The problems arise because your hardware (SM) supports TXDONE_BY_POLL,
but your client drives it by TXDONE_BY_ACK because the older DB
channels are so.

Please populate SM channels as a separate controller than DB.
The DB controller, as is, run by ACK method.
The SM controller should be run by polling, i.e, set txdone_poll =
true and the poll period small enough. The virtual tty client driver
should be able to safely set tx_block from appropriate context.

Sorry, I should have clarified that I already split up the controllers. The SM controller has txdone_poll = true. I didn't adjust txpoll_period so I guess it's zero.