linux-kernel - Re: [Patch v4 2/2] firmware: qcom: scm: Fix interrupted SCM calls

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Date:   Sun, 29 Jan 2017 16:24:51 -0800
From:   Olof Johansson <olof@...om.net>
To:     Andy Gross <andy.gross@...aro.org>
Cc:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Will Deacon <will.deacon@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Kevin Hilman <khilman@...libre.com>,
        Russell King <linux@...linux.org.uk>
Subject: Re: [Patch v4 2/2] firmware: qcom: scm: Fix interrupted SCM calls

Hi,

On Thu, Jan 19, 2017 at 8:58 AM, Andy Gross <andy.gross@...aro.org> wrote:
> This patch adds a Qualcomm specific quirk to the arm_smccc_smc call.
>
> On Qualcomm ARM64 platforms, the SMC call can return before it has
> completed.  If this occurs, the call can be restarted, but it requires
> using the returned session ID value from the interrupted SMC call.
>
> The quirk stores off the session ID from the interrupted call in the
> quirk structure so that it can be used by the caller.
>
> This patch folds in a fix given by Sricharan R:
> https://lkml.org/lkml/2016/9/28/272
>
> Signed-off-by: Andy Gross <andy.gross@...aro.org>
> Reviewed-by: Will Deacon <will.deacon@....com>
> ---
>  arch/arm64/kernel/smccc-call.S |  9 ++++++++-
>  drivers/firmware/qcom_scm-64.c | 13 ++++++++++---
>  include/linux/arm-smccc.h      | 11 ++++++++---
>  3 files changed, 26 insertions(+), 7 deletions(-)
>
> diff --git a/arch/arm64/kernel/smccc-call.S b/arch/arm64/kernel/smccc-call.S
> index 6290696..72ecdca 100644
> --- a/arch/arm64/kernel/smccc-call.S
> +++ b/arch/arm64/kernel/smccc-call.S
> @@ -12,6 +12,7 @@
>   *
>   */
>  #include <linux/linkage.h>
> +#include <linux/arm-smccc.h>
>  #include <asm/asm-offsets.h>
>
>         .macro SMCCC instr
> @@ -20,7 +21,13 @@
>         ldr     x4, [sp]
>         stp     x0, x1, [x4, #ARM_SMCCC_RES_X0_OFFS]
>         stp     x2, x3, [x4, #ARM_SMCCC_RES_X2_OFFS]
> -       ret
> +       ldr     x4, [sp, #8]
> +       cbz     x4, 1f /* no quirk structure */
> +       ldr     x9, [x4, #ARM_SMCCC_QUIRK_ID_OFFS]
> +       cmp     x9, #ARM_SMCCC_QUIRK_QCOM_A6
> +       b.ne    1f
> +       str     x6, [x4, ARM_SMCCC_QUIRK_STATE_OFFS]
> +1:     ret
>         .cfi_endproc
>         .endm

This extends the SMC entry/return path quite a bit.

Is this truly a qualcomm-only quirk, or are other vendors also picking it up?

Why not either make arm_smccc_.* function pointers and update them
accordingly, or use a custom version for the specific locations where
you want/need to restart the calls? You are after all already wrapping
them in qcom_scm_call().

Seems like a more appropriate change than burden all platforms with
longer code path due to your quirk.


-Olof