On Thu, Jul 26, 2018 at 5:21 PM, A.s. Dong <aisheng.dong@xxxxxxx> wrote: > Hi Jassi, > >> -----Original Message----- >> From: Jassi Brar [mailto:jassisinghbrar@xxxxxxxxx] >> Sent: Thursday, July 26, 2018 5:50 PM >> To: Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx> >> Cc: Shawn Guo <shawnguo@xxxxxxxxxx>; Fabio Estevam >> <fabio.estevam@xxxxxxx>; Rob Herring <robh+dt@xxxxxxxxxx>; Mark >> Rutland <mark.rutland@xxxxxxx>; A.s. Dong <aisheng.dong@xxxxxxx>; >> Vladimir Zapolskiy <vladimir_zapolskiy@xxxxxxxxxx>; , Sascha Hauer >> <kernel@xxxxxxxxxxxxxx>; , linux-arm-kernel@xxxxxxxxxxxxxxxxxxx, linux- >> mediatek@xxxxxxxxxxxxxxxxxxx, srv_heupstream <linux-arm- >> kernel@xxxxxxxxxxxxxxxxxxx>; Devicetree List <devicetree@xxxxxxxxxxxxxxx>; >> dl-linux-imx <linux-imx@xxxxxxx> >> Subject: Re: [PATCH v7 3/6] dt-bindings: mailbox: imx-mu: add generic MU >> channel support >> >> On Thu, Jul 26, 2018 at 12:23 PM, Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx> >> wrote: >> >> > Each MU has four pairs of rx/tx data register with four rx/tx >> > interrupts which can also be used as a separate channel. >> > >> So the hardware actually supports 4 channels. >> >> > -- #mbox-cells: Must be 0. Number of cells in a mailbox >> > +- #mbox-cells: Must be: >> > + 0 - for single channel mode. i.MX8* SCU protocol specific. >> > + 1 - for multichannel (generic) mode. >> > + >> No, please. >> DT bindings should reflect the real hardware, and not the software mode we >> want the driver to work in. >> Please define mbox-cells=1 and have the i.MX8* platform always ask for >> channel-0. > > The reality is that MU hardware does not define channels in reference manual. > However, it does have four separate data tx/rx register which can be used > as 'virtual' channels which is supported by this current driver. > > See below HW description from the reference manual: > For messaging, the MU has four, 32-bit write-only transmit registers and four, 32-bit > read-only receive registers on the Processor B and Processor A-sides. These registers are > used for sending messages to each other. > > 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; the message’s first three words are written to the registers whose > interrupt is masked, and the fourth word is written to the other register (which > triggers an interrupt at the receiver side). > > The reference manual is at here: (Chapter 42 Messaging Unit (MU) > https://www.nxp.com/docs/en/reference-manual/IMX6ULRM.pdf > Thanks. That makes life much easier. > And SCU firmware does use MU in above way specified by reference manual. > Even from HW point of view, it's still one channel only mailbox. > That's why we change the mbox-cells to 0 accordingly to avoid confusing > the multi channels users supported in this driver. > > As per Sasha's request, we're going to support both protocol (SCU and generic M4) > in one mailbox driver, that means we need deal with this two case property. > > If we use mbox-cells 1 case for SCU, then the using would be like: > mboxes = <&mailbox 0> which is mixed with the normal multi channel > users. And we also must state clearly in binding doc that for mbox-cells > 1 case for SCU, the cell value must be 0 which is also confusing with > Multi channel users. > > How do you suggest for such case? > Let me read the spec and try to see/shine the light :) Cheers! -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
