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

[Mikko Perttunen]

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>
> > > > wrote:
> > > > > 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
> > > > > data.
> > > > 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.

Mikko