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    SubjectRe: [PATCH v3 3/8] mailbox: Add transmit done by blocking option
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    On 08/08/2018 05:10 PM, Jassi Brar wrote:
    > On Wed, Aug 8, 2018 at 5:08 PM, Mikko Perttunen <cyndis@kapsi.fi> 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@nvidia.com>
    >>>> 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

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