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

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Date:   Wed, 8 Aug 2018 20:09:16 +0530
From:   Jassi Brar <jassisinghbrar@...il.com>
To:     Mikko Perttunen <cyndis@...si.fi>
Cc:     Mikko Perttunen <mperttunen@...dia.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Jon Hunter <jonathanh@...dia.com>,
        Devicetree List <devicetree@...r.kernel.org>,
        linux-serial@...r.kernel.org, linux-tegra@...r.kernel.org,
        <", linux-arm-kernel"@lists.infradead.org>,
        srv_heupstream <linux-mediatek@...ts.infradead.org>,
        srv_heupstream <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 3/8] mailbox: Add transmit done by blocking option

On Wed, Aug 8, 2018 at 8:04 PM, Mikko Perttunen <cyndis@...si.fi> wrote:
>
>
> On 08/08/2018 05:10 PM, Jassi Brar wrote:
>>
>> On Wed, Aug 8, 2018 at 5:08 PM, Mikko Perttunen <cyndis@...si.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@...dia.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.