linux-kernel - RE: [PATCH V6 0/4] mailbox/firmware: imx: support SCU channel type

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Date:   Wed, 18 Mar 2020 12:14:31 +0000
From:   Peng Fan <peng.fan@....com>
To:     Leonard Crestez <leonard.crestez@....com>,
        "jassisinghbrar@...il.com" <jassisinghbrar@...il.com>,
        "o.rempel@...gutronix.de" <o.rempel@...gutronix.de>
CC:     "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        dl-linux-imx <linux-imx@....com>,
        Anson Huang <anson.huang@....com>,
        Aisheng Dong <aisheng.dong@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH V6 0/4] mailbox/firmware: imx: support SCU channel type

> Subject: Re: [PATCH V6 0/4] mailbox/firmware: imx: support SCU channel
> type
> 
> On 2020-03-13 9:38 AM, Peng Fan wrote:
> >> Subject: RE: [PATCH V6 0/4] mailbox/firmware: imx: support SCU
> >> channel type
> >>
> >> Hi Leonard,
> >>
> >>> Subject: Re: [PATCH V6 0/4] mailbox/firmware: imx: support SCU
> >>> channel type
> >>>
> >>> On 2020-03-04 7:55 AM, Peng Fan wrote:
> >>>> From: Peng Fan <peng.fan@....com>
> >>>>
> >>>> V6:
> >>>>    Add Oleksij's R-b tag
> >>>>    Patch 3/4, per
> >>> https://www.kernel.org/doc/Documentation/printk-formats.txt
> >>>>    should use %zu for printk sizeof
> >>>>
> >>>> V5:
> >>>>    Move imx_mu_dcfg below imx_mu_priv
> >>>>    Add init hooks to imx_mu_dcfg
> >>>>    drop __packed __aligned
> >>>>    Add more debug msg
> >>>>    code style cleanup
> >>>>
> >>>> V4:
> >>>>    Drop IMX_MU_TYPE_[GENERIC, SCU]
> >>>>    Pack MU chans init to separate function
> >>>>    Add separate function for SCU chans init and xlate
> >>>>    Add santity check to msg hdr.size
> >>>>    Limit SCU MU chans to 6, TX0/RX0/RXDB[0-3]
> >>>>
> >>>> V3:
> >>>>    Rebase to Shawn's for-next
> >>>>    Include fsl,imx8-mu-scu compatible
> >>>>    Per Oleksij's comments, introduce generic tx/rx and added scu mu
> type
> >>>>    Check fsl,imx8-mu-scu in firmware driver for fast_ipc
> >>>>
> >>>> V2:
> >>>>    Drop patch 1/3 which added fsl,scu property
> >>>>    Force to use scu channel type when machine has node compatible
> >>> "fsl,imx-scu"
> >>>>    Force imx-scu to use fast_ipc
> >>>>
> >>>>    I not found a generic method to make SCFW message generic
> >>>> enough,
> >>> SCFW
> >>>>    message is not fixed length including TX and RX. And it use TR0/RR0
> >>>>    interrupt.
> >>>>
> >>>> V1:
> >>>> Sorry to bind the mailbox/firmware patch together. This is make it
> >>>> to understand what changed to support using 1 TX and 1 RX channel
> >>>> for SCFW message.
> >>>>
> >>>> Per i.MX8QXP Reference mannual, there are several message using
> >>>> examples. One of them is:
> >>>> Passing short messages: Transmit register(s) can be used to pass
> >>>> short messages from one to four words in length. For example, when
> >>>> a four-word message is desired, only one of the registers needs to
> >>>> have its corresponding interrupt enable bit set at the receiver side.
> >>>>
> >>>> This patchset is to using this for SCFW message to replace four TX
> >>>> and four RX method.
> >>>
> >>> Tested-by: Leonard Crestez <leonard.crestez@....com>
> >>>
> >>
> >> Thanks for the test.
> >>
> >>> My stress tests pass on imx8qxp with this patcheset, however
> >>> performance is not greatly improved. My guess is that this happens
> >>> because of too many interrupts.
> >>
> >> Might be. Could you share your testcase?
> 
> https://github.com/cdleonard/imx-scu-test
> 
> >>> Is there really a reason to enable TIE? Spinning on TE bits without
> >>> any interrupts should be just plain faster.
> >>
> >> I could try to disable TIE and give a try. If performance improves
> >> lot, I could change to non TX interrupt.
> >
> > After rethinking about this, we need TX interrupt, otherwise we have
> > to use TX_POLL which is slower or let the client kick the TX state machine.
> >
> > Compared with original method, this already reduces to use 1 TX and 1
> > RX interrupt. This already good for system.
> 
> Sorry, I missed that fact that your patches don't include the required DTS
> changes. Indeed that is only one TX and one RX irq per call now.
> 
> Running my test now results in RX timeout :(

Might be long that 4 word messages, because not check TX empty
and RX full in my patch.

> 
> -----
> 
> On an unrelated note: are you sure it is appropriate to change the compat
> string here? Another way to implement direct SCU communication would be
> as another channel type, IMX_MU_TYPE_SCUTX.

No. This will introduce more complexity. Per Oleksij's suggestion, I added
the compatible string.

> 
> It also strange that you're adding a bool fast_ipc in imx-scu, do we really want
> to support the old path?

It is to avoid break DT backward compatibility.

Thanks,
Peng.

> 
> If SCU protocol was implemented as a channel type then maybe we could
> sidestep mbox_request_channel_by_name, parse mboxes manually and
> always request MU_TYPE_SCUTX.
> 
> --
> Regards,
> Leonard