linux-kernel - Re: [PATCH 3/3] soc: xilinx: zynqmp: Add firmware interface

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Date:   Thu, 17 Aug 2017 23:11:45 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Michal Simek <michal.simek@...inx.com>
Cc:     Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Sören Brinkmann <soren.brinkmann@...inx.com>,
        Lucas Stach <l.stach@...gutronix.de>,
        Michal Simek <monstr@...str.eu>, yangbo lu <yangbo.lu@....com>,
        Andreas Färber <afaerber@...e.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
        Baoyou Xie <baoyou.xie@...aro.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Simon Horman <horms+renesas@...ge.net.au>
Subject: Re: [PATCH 3/3] soc: xilinx: zynqmp: Add firmware interface

On Thu, Aug 17, 2017 at 12:48 PM, Michal Simek <michal.simek@...inx.com> wrote:
> On 16.8.2017 17:05, Arnd Bergmann wrote:
>> On Wed, Aug 16, 2017 at 4:34 PM, Michal Simek <michal.simek@...inx.com> wrote:
>>
>> Looks good, just make sure you also check with sparse (make C=1)
>> to ensure you have the right __le64/__le32 types everywhere.
>
> Are you aware about any doc where it is written that data should be
> passed as little endian?

Looking at http://infocenter.arm.com/help/topic/com.arm.doc.den0028b/ARM_DEN0028B_SMC_Calling_Convention.pdf
now, I think that the structure above is endian-neutral as the arguments
get passed in registers rather than memory.

However, if you pass pointers to data structures in memory, those
data structures would have to be defined with __le32/__le64 types.

> I was playing with it a little bit and this means that these 2(3 with
> hvc) needs to be changed.
>
> asmlinkage void __arm_smccc_smc(__le64 a0, __le64 a1, __le64 a2,
>  __le64 a3,__le64 a4, __le64 a5, __le64 a6, __le64 a7,
> struct arm_smccc_res *res, struct arm_smccc_quirk *quirk);
>
>  struct arm_smccc_res {
> -       unsigned long a0;
> -       unsigned long a1;
> -       unsigned long a2;
> -       unsigned long a3;
> +       __le64 a0;
> +       __le64 a1;
> +       __le64 a2;
> +       __le64 a3;
>  };

This is clearly wrong on 32-bit machines, I think this is intentionally
defined as 'unsigned long' to have register sized arguments.

       Arnd