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Subject: Re: [PATCH v3 3/8] mailbox: Add transmit done by blocking option
From:   Mikko Perttunen <cyndis@kapsi.fi>
To:     Jassi Brar <jassisinghbrar@gmail.com>,
        Mikko Perttunen <mperttunen@nvidia.com>
Cc:     Greg KH <gregkh@linuxfoundation.org>,
        Thierry Reding <thierry.reding@gmail.com>,
        Jon Hunter <jonathanh@nvidia.com>,
        Devicetree List <devicetree@vger.kernel.org>,
        linux-serial@vger.kernel.org, linux-tegra@vger.kernel.org,
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        srv_heupstream <linux-arm-kernel@lists.infradead.org>,
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References: <20180702114033.15654-1-mperttunen@nvidia.com>
 <20180702114033.15654-4-mperttunen@nvidia.com>
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Date:   Wed, 8 Aug 2018 14:38:28 +0300
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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?

Thanks,
Mikko

> 
>>
>> 2) Implementing TEGRA_HSP_MBOX_TYPE_SM :-
>>         In mailbox framework, a controller is a collection of identical
>> channels. That is, instances of the same class.
>>         So ideally, in probe you should populate a controller for each
>> type of channel, i.e, DB, SM, SS and AS.
> 
> Hmm, yes, I guess this would be possible if I change the mailbox core to 
> allow registering multiple controllers per device.
> 
> Thanks!
> Mikko
> 
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