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From:   Jassi Brar <jassisinghbrar@gmail.com>
Date:   Thu, 9 Aug 2018 14:56:56 +0530
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Subject: Re: [PATCH v3 3/8] mailbox: Add transmit done by blocking option
To:     Mikko Perttunen <cyndis@kapsi.fi>
Cc:     Mikko Perttunen <mperttunen@nvidia.com>,
        Greg KH <gregkh@linuxfoundation.org>,
        Thierry Reding <thierry.reding@gmail.com>,
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[dropping everyone else while we discuss the code]

Thanks. I assume that branch as all the code that there is. Let me
look and get back to you.

On Thu, Aug 9, 2018 at 2:19 PM, Mikko Perttunen <cyndis@kapsi.fi> wrote:
> Here's my current code:
>
> https://github.com/cyndis/linux/commits/wip/t194-tcu-4
>
> "fixup! mailbox: tegra-hsp: Add support for shared mailboxes" splits up the
> controller into two. "tegra-hsp: use polling" changes it to use polling.
>
> There are two lines in the top patch with comments:
>
> - at the end of tegra_hsp_mailbox_send_data, I left a "while
> (!tegra_hsp_mailbox_last_tx_done(chan));". Without it I wasn't able to see
> even a few garbled characters in the output.
>
> - as mentioned, if I enable tx_block on the client side, I get a BUG:
> scheduling while atomic. I assume this gets printed through the earlycon as
> it's printing out correctly.
>
> Thanks,
> Mikko
>
>
> On 08.08.2018 17:46, Mikko Perttunen wrote:
>>
>> On 08/08/2018 05:39 PM, Jassi Brar wrote:
>>>
>>> On Wed, Aug 8, 2018 at 8:04 PM, Mikko Perttunen <cyndis@kapsi.fi> wrote:
>>>>
>>>>
>>>>
>>>> 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.
>>>>
>>> Can you please share your code (controller and client) ? Maybe offline
>>> if you wish.
>>>
>>
>> I'll upload a git branch tomorrow -- I'm not at the machine with the code
>> now.
>>
>> Mikko
>> --
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