RE: [PATCH v1 3/3] remoteproc: Add Renesas rcar driver

Hi Julien,

Subject: Re: [PATCH v1 3/3] remoteproc: Add Renesas rcar driver

Hi Biju,

quoted

One question CR7 Can be master boot processor. In that case How to
avoid loading and booting  CR7 processor from Linux?
Reading boot modes??

Thanks for the question.

I did not test this case. 

OK.

There is also other scenarios where the

Cortex-R7 is started by an earlier component such as BL2, u-boot or OP-
Tee.
In these cases Linux should not try to start / stop this remote processor.

OK. But Linux can check whether CR7 is alive at frequent interval and issue
Soft-reboot, if there is a  hang.

One idea could be to read the power status CR7PSTR / PWRSR7, or use one of
the MFIS register as a communication register.

I know MFIS is used for communication between CR7 and CA-57. But don't know
much details.

STM32 processor use this

last solution to indicate that the remote processor is already started, in
that scenario remoteproc driver starts in 'detached' state instead of
'offline' state.
https://jpn01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgit.kern
el.org%2Fpub%2Fscm%2Flinux%2Fkernel%2Fgit%2Ftorvalds%2Flinux.git%2Ftree%2F
include%2Flinux%2Fremoteproc.h%23n418&data=04%7C01%7Cbiju.das.jz%40bp.
renesas.com%7C945a25980e5a49cc361a08d9a846020c%7C53d82571da1947e49cb4625a1
66a4a2a%7C0%7C0%7C637725840924834250%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wL
jAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=yXH
2qBpmUI2YtZRnApFdWt6iONcFKDPSPa45AirThBw%3D&reserved=0

In that state, remoteproc driver can initiate communication with this
remote processor but will not try to start or to stop it.

That's something I have in mind, with an existing implementation there
https://jpn01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.c
om%2Fiotbzh%2Flinux%2Fblob%2Fiot%2Fjulien%2Frproc%2Fdrivers%2Fremoteproc%2
Frcar_rproc.c%23L524&data=04%7C01%7Cbiju.das.jz%40bp.renesas.com%7C945
a25980e5a49cc361a08d9a846020c%7C53d82571da1947e49cb4625a166a4a2a%7C0%7C0%7
C637725840924834250%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2
luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=WYKygEUiXyliOmX2CUxk
Yfj5pq2QOmZC%2BGtXRAlB%2Bws%3D&reserved=0
(that is not ready for upstream yet :)).

I guess this issue also exists when one device is dedicated to the secure
world, so the device exists, but not available for Linux. 

May be for prototyping activity, if some one wants to run an RTOS on CR7.
This will be a good solution. Linux will load and boot CR7 which
Run an RTOS which communicates with Linux. Once communication established
Linux can check the health of CR7 at frequent intervals and take necessary action.

Regards,
Biju


The most obvious

(and dirty ?) solution is to keep the device disabled in dts.

Regards,
Julien