From: "Andrew F. Davis" <afd@ti.com>
To: Tony Lindgren <tony@atomide.com>
Cc: Mark Rutland <mark.rutland@arm.com>, <linux-omap@vger.kernel.org>,
<linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] ARM: OMAP: Use ARM SMC Calling Convention when OP-TEE is available
Date: Tue, 19 Nov 2019 14:35:26 -0500 [thread overview]
Message-ID: <0ad31b32-712e-5bef-5645-0336dfec99cc@ti.com> (raw)
In-Reply-To: <20191119192029.GP35479@atomide.com>
On 11/19/19 2:20 PM, Tony Lindgren wrote:
> * Andrew F. Davis <afd@ti.com> [191119 19:13]:
>> On 11/19/19 2:07 PM, Tony Lindgren wrote:
>>> * Andrew F. Davis <afd@ti.com> [191119 18:51]:
>>>> On 11/19/19 1:32 PM, Tony Lindgren wrote:
>>>>> It would allow us to completely change over to using
>>>>> arm_smccc_smc() and forget the custom calls.
>>>>
>>>> We would need more than just the r12 quirk to replace all our custom SMC
>>>> handlers, we would need quirks for omap_smc2 which puts process ID in r1
>>>> and puts #0xff in r6, and omap_smc3 that uses smc #1. All of our legacy
>>>> SMC calls also trash r4-r11, that is very non SMCCC complaint as only
>>>> r4-r7 need be caller saved. I don't see arm_smccc_smc() working with
>>>> legacy ROM no matter how much we hack at it :(
>>>
>>> We would just have omap_smc2() call arm_smccc_smc() and in that
>>> case. And omap_smc2() would still deal with saving and restoring
>>> the registers.
>>
>> Then why call arm_smccc_smc()? omap_smc2() is already an assembly
>> function, all it needs to do after loading the registers and saving the
>> right ones is issue an "smc #0" instruction, why would we want to
>> instead call into some other function to re-save registers and issue the
>> exact same instruction?
>
> To use Linux generic API for smc calls where possible.
>
But we are not using generic API calls, we are using omap_smcx() which
cannot call into arm_smccc_smc(). For all the above reasons plus
arm_smccc_smc() uses r12 to save the stack pointer, our ROM expects r12
to store the function ID.
>>> Certainly the wrapper functions calling arm_smccc_smc() can deal
>>> with r12 too if the r12-quirk version and the plain version are
>>> never needed the same time on a booted SoC.
>>>
>>> Are they ever needed the same time on a booted SoC or not?
>
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
They should not be needed at the same time, either OP-TEE is on the
secure side or ROM is there.
Andrew
> Sorry but maybe check the font size on your screen. I'm trying to
> get your attention again for the second time above to answer a
> question I asked.
>
>>>> I can make OP-TEE also compatible with the r12 quirk, which is what I
>>>> used to do. That way we didn't need to do any detection. The issue was
>>>> that non-standard SMC calls should not go through the common SMCCC
>>>> handler (unless you are QCOM for some reason..).
>>>
>>> Sounds like for optee nothing must be done for r12 :)
>
>> Unless all our calls use the r12 hack, then we would need to fixup
>> OP-TEE to accept that also.
>
> No idea about that that part, but sounds like r12 use is up to
> the caller in the optee case.
>
> Regards,
>
> Tony
>
next prev parent reply other threads:[~2019-11-19 19:35 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-18 16:52 [PATCH] ARM: OMAP: Use ARM SMC Calling Convention when OP-TEE is available Andrew F. Davis
2019-11-18 21:57 ` Tony Lindgren
2019-11-18 22:13 ` Andrew F. Davis
2019-11-18 22:31 ` Tony Lindgren
2019-11-19 1:13 ` Andrew F. Davis
2019-11-19 16:21 ` Tony Lindgren
2019-11-19 16:30 ` Tony Lindgren
2019-11-19 16:30 ` Andrew F. Davis
2019-11-19 16:42 ` Tony Lindgren
2019-11-19 18:05 ` Tony Lindgren
2019-11-19 18:20 ` Andrew F. Davis
2019-11-19 18:32 ` Tony Lindgren
2019-11-19 18:50 ` Andrew F. Davis
2019-11-19 19:07 ` Tony Lindgren
2019-11-19 19:12 ` Andrew F. Davis
2019-11-19 19:20 ` Tony Lindgren
2019-11-19 19:35 ` Andrew F. Davis [this message]
2019-11-19 19:44 ` Tony Lindgren
2019-11-19 19:59 ` Andrew F. Davis
2019-12-16 20:56 ` Andrew F. Davis
2019-12-16 21:04 ` Tony Lindgren
2019-12-16 22:34 ` Andrew F. Davis
2019-12-16 22:41 ` Tony Lindgren
2019-12-17 13:14 ` Andrew F. Davis
2019-12-17 15:07 ` Tony Lindgren
2019-12-17 17:01 ` Andrew F. Davis
2019-12-17 17:11 ` Tony Lindgren
2019-12-17 17:18 ` Tony Lindgren
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=0ad31b32-712e-5bef-5645-0336dfec99cc@ti.com \
--to=afd@ti.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-omap@vger.kernel.org \
--cc=mark.rutland@arm.com \
--cc=tony@atomide.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).