linux-kernel - Re: [PATCH V4 3/5] mailbox: imx: add imx mu support

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Message-ID: <CABb+yY0XQwXjVUMiXcqFVVCTR2jRWA343d220LqBYmTp+s6J1Q@mail.gmail.com>
Date:   Wed, 11 Jul 2018 22:30:32 +0530
From:   Jassi Brar <jassisinghbrar@...il.com>
To:     "A.s. Dong" <aisheng.dong@....com>
Cc:     Sascha Hauer <s.hauer@...gutronix.de>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "dongas86@...il.com" <dongas86@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Oleksij Rempel <o.rempel@...gutronix.de>,
        dl-linux-imx <linux-imx@....com>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        Fabio Estevam <fabio.estevam@....com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>
Subject: Re: [PATCH V4 3/5] mailbox: imx: add imx mu support

On Wed, Jul 11, 2018 at 10:11 PM, A.s. Dong <aisheng.dong@....com> wrote:
> Hi Jassi,
>
>> -----Original Message-----
>> From: Jassi Brar [mailto:jassisinghbrar@...il.com]
>> Sent: Thursday, July 12, 2018 12:32 AM
>> To: A.s. Dong <aisheng.dong@....com>
>> Cc: Sascha Hauer <s.hauer@...gutronix.de>; linux-arm-
>> kernel@...ts.infradead.org; dongas86@...il.com; linux-
>> kernel@...r.kernel.org; Oleksij Rempel <o.rempel@...gutronix.de>; dl-
>> linux-imx <linux-imx@....com>; kernel@...gutronix.de; Fabio Estevam
>> <fabio.estevam@....com>; shawnguo@...nel.org
>> Subject: Re: [PATCH V4 3/5] mailbox: imx: add imx mu support
>>
>> On Wed, Jul 11, 2018 at 6:28 PM, A.s. Dong <aisheng.dong@....com> wrote:
>> > Hi Jassi,
>> >
>> >> -----Original Message-----
>> >> From: Jassi Brar [mailto:jassisinghbrar@...il.com]
>> >> Sent: Wednesday, July 11, 2018 6:44 PM
>> >> To: A.s. Dong <aisheng.dong@....com>
>> >> Cc: Sascha Hauer <s.hauer@...gutronix.de>; linux-arm-
>> >> kernel@...ts.infradead.org; dongas86@...il.com; linux-
>> >> kernel@...r.kernel.org; Oleksij Rempel <o.rempel@...gutronix.de>; dl-
>> >> linux-imx <linux-imx@....com>; kernel@...gutronix.de; Fabio Estevam
>> >> <fabio.estevam@....com>; shawnguo@...nel.org
>> >> Subject: Re: [PATCH V4 3/5] mailbox: imx: add imx mu support
>> >>
>> >> On Wed, Jul 11, 2018 at 4:07 PM, A.s. Dong <aisheng.dong@....com>
>> wrote:
>> >> >
>> >> > > -----Original Message-----
>> >> > > From: Sascha Hauer [mailto:s.hauer@...gutronix.de]
>> >> > > Sent: Wednesday, July 11, 2018 3:55 PM
>> >> > > To: A.s. Dong <aisheng.dong@....com>
>> >> > > Cc: linux-arm-kernel@...ts.infradead.org; dongas86@...il.com;
>> >> > > Jassi Brar <jassisinghbrar@...il.com>;
>> >> > > linux-kernel@...r.kernel.org; Oleksij Rempel
>> >> > > <o.rempel@...gutronix.de>; dl-linux-imx <linux-imx@....com>;
>> >> > > kernel@...gutronix.de; Fabio Estevam <fabio.estevam@....com>;
>> >> > > shawnguo@...nel.org
>> >> > > Subject: Re: [PATCH V4 3/5] mailbox: imx: add imx mu support
>> >> > >
>> >> > > On Wed, Jul 11, 2018 at 07:29:38AM +0000, A.s. Dong wrote:
>> >> > > > Hi Sascha,
>> >> > > >
>> >> > > > > -----Original Message-----
>> >> > > > > From: Sascha Hauer [mailto:s.hauer@...gutronix.de]
>> >> > > > > Sent: Tuesday, July 10, 2018 10:20 PM
>> >> > > > > To: A.s. Dong <aisheng.dong@....com>
>> >> > > > > Cc: linux-arm-kernel@...ts.infradead.org; dongas86@...il.com;
>> >> > > > > Jassi Brar <jassisinghbrar@...il.com>;
>> >> > > > > linux-kernel@...r.kernel.org; Oleksij Rempel
>> >> > > > > <o.rempel@...gutronix.de>; dl-linux-imx <linux-imx@....com>;
>> >> > > > > kernel@...gutronix.de; Fabio Estevam
>> <fabio.estevam@....com>;
>> >> > > > > shawnguo@...nel.org
>> >> > > > > Subject: Re: [PATCH V4 3/5] mailbox: imx: add imx mu support
>> >> > > > >
>> >> > > > > Hi,
>> >> > > > >
>> >> > > > > On Sun, Jul 08, 2018 at 10:56:55PM +0800, Dong Aisheng wrote:
>> >> > > > > > This is used for i.MX multi core communication.
>> >> > > > > > e.g. A core to SCU firmware(M core) on MX8.
>> >> > > > > >
>> >> > > > > > Tx is using polling mode while Rx is interrupt driven and
>> >> > > > > > schedule a hrtimer to receive remain words if have more
>> >> > > > > > than
>> >> > > > > > 4 words.
>> >> > > > >
>> >> > > > > You told us that using interrupts is not possible due to
>> >> > > > > miserable performance, we then provided you a way with which
>> >> > > > > you
>> >> could poll.
>> >> > > > > Why are you using interrupts now?
>> >> > > > >
>> >> > > >
>> >> > > > Because mailbox framework does not support sync rx now, I think
>> >> > > > we do not need to wait for that feature done first as it's
>> >> > > > independent and separate features of framework.
>> >> > >
>> >> > > You can wait forever for this feature, nobody will add it for you.
>> >> > > It's up to you to add support for that feature. Who else should
>> >> > > add this
>> >> feature if not you?
>> >> > > And when will you add that feature if not now when you actually need
>> it?
>> >> > > It is common practice that you adjust the frameworks to your
>> >> > > needs rather than working around them.
>> >> > >
>> >> >
>> >> > I'm willing to add it. Just because you said Jassi already had the
>> >> > idea on how to Implement it and does not add much complexity. So I
>> >> > just
>> >> want to see his patches.
>> >> > But if he did not work on it, I can also help on it.
>> >> >
>> >> I am not much aware of the history of this conversation... but it
>> >> seems you need to make use of mbox_chan_ops.peek_data().
>> >>
>> >> If not that, please let me know the requirement.
>> >>
>> >
>> > Thanks for the suggestion.
>> > It looks to me may work.
>> >
>> > From the definition, it seems it's used to pull data from remote side.
>> > /**
>> >  * mbox_client_peek_data - A way for client driver to pull data
>> >  *                      received from remote by the controller.
>> >  * @chan: Mailbox channel assigned to this client.
>> >  *
>> >  * A poke to controller driver for any received data.
>> >  * The data is actually passed onto client via the
>> >  * mbox_chan_received_data()
>> >  * The call can be made from atomic context, so the controller's
>> >  * implementation of peek_data() must not sleep.
>> >  *
>> >  * Return: True, if controller has, and is going to push after this,
>> >  *          some data.
>> >  *         False, if controller doesn't have any data to be read.
>> >  */
>> > bool mbox_client_peek_data(struct mbox_chan *chan) {
>> >         if (chan->mbox->ops->peek_data)
>> >                 return chan->mbox->ops->peek_data(chan);
>> >
>> >         return false;
>> > }
>> > EXPORT_SYMBOL_GPL(mbox_client_peek_data);
>> > But it seems most users in kernel simply implement it as a data
>> > available Checking rather than receiving it.
>> > See:
>> > drivers/mailbox/ti-msgmgr.c
>> > drivers/mailbox/mailbox-altera.c
>> >
>> > Only bcm uses it to receive data.
>> > drivers/mailbox/bcm-flexrm-mailbox.c
>> >
>> > For our requirement, we want to implement sync receiving protocol like:
>> > Sc_call_rpc()
>> > {
>> >         mbox_send_message(chan, msg)
>> >         If (!no_resp)
>> >                 // rx also stored in msg
>> >                 mbox_receive_msg_in_polling(chan, msg);
>> >         mbox_client_txdone();
>> > }
>> >
>> > If using peek_data, it can be:
>> > Sc_call_rpc()
>> > {
>> >         mbox_send_message(chan, msg)
>> >         If (!no_resp)
>> >                 // rx also stored in msg
>> >                 Mbox_client_peek_data(chan);
>> >
>> Yes, and you may want to loop for a certain amount of time if peek keeps
>> returning false.
>>
>> >         mbox_client_txdone();
>> > }
>> >
>> > And for mu controller driver .peek_data():
>> > imx_mu_peek_data(chan)
>> > {
>> >         // get first word and parse data size
>> >         imx_mu_receive_msg(&mu->chans, 0, mu->msg);
>> >
>> >         raw_data = (u8 *)mu->msg;
>> >         size = raw_data[1];
>> >
>> >         // receive rest of them
>> >         for (i = 1; i < size; i++) {
>> >                 ret = imx_mu_receive_msg(&mu->chans, i % 4, mu->msg + i);
>> >                 if (ret)
>> >                         return false;
>> >         }
>> >
>> >         mbox_chan_received_data(&mu->chans, (void *)mu->msg);
>> >
>> Not sure how your controller works. But the peek() callback only _checks_ if
>> there is some data available to be read. Please note that
>> peek() can not sleep.
>> So if the data fetching doesn't sleep you can do that here, otherwise peek
>> has to schedule the actual fetching of data from remote and providing to the
>> client via mbox_chan_received_data.
>>
>
> bcm seems is using peek to receive data, not only checking the data availability,
> right?
> drivers/mailbox/bcm-flexrm-mailbox.c
>
As I said, if fetching data from remote don't need to sleep, you can
call mbox_chan_received_data() from peek(). Otherwise not.