linux-kernel - Re: [PATCH v4 4/4] firmware: arm_scmi: Add qcom hvc/shmem transport support

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Message-ID: <20231005222016.GI3553829@hu-bjorande-lv.qualcomm.com>
Date:   Thu, 5 Oct 2023 15:20:16 -0700
From:   Bjorn Andersson <quic_bjorande@...cinc.com>
To:     Sudeep Holla <sudeep.holla@....com>
CC:     Nikunj Kela <quic_nkela@...cinc.com>, <cristian.marussi@....com>,
        <robh+dt@...nel.org>, <krzysztof.kozlowski+dt@...aro.org>,
        <conor+dt@...nel.org>, <andersson@...nel.org>,
        <konrad.dybcio@...aro.org>, <linux-arm-kernel@...ts.infradead.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCH v4 4/4] firmware: arm_scmi: Add qcom hvc/shmem transport
 support

On Wed, Oct 04, 2023 at 05:06:30PM +0100, Sudeep Holla wrote:
> On Tue, Oct 03, 2023 at 09:16:27AM -0700, Nikunj Kela wrote:
> > On 10/3/2023 4:19 AM, Sudeep Holla wrote:
> > > On Mon, Sep 11, 2023 at 12:43:59PM -0700, Nikunj Kela wrote:
> > > > diff --git a/drivers/firmware/arm_scmi/smc.c b/drivers/firmware/arm_scmi/smc.c
[..]
> > > > @@ -63,6 +66,8 @@ struct scmi_smc {
> > > >   	u32 func_id;
> > > >   	u32 param_page;
> > > >   	u32 param_offset;
> > > > +	u64 cap_id;
> > > Can it be unsigned long instead so that it just works for both 32 and 64 bit.
> > 
> > My first version of this patch was ulong but Bjorn suggested to make this
> > structure size fixed i.e. architecture independent. Hence changed it to u64.
> > If you are ok with ulong, I can change it back to ulong.
> >
> 
> SMCCC pre-v1.2 used the common structure in that way. I don't see any issue
> with that. I haven't followed Bjorn suggestions/comments though.
> 

My request was that funcId and capId is an ABI between the firmware and
the OS, so I'd like for that to use well defined, fixed sized, data
types - if nothing else just for documentation purpose.

These values will be truncated when passed to arm_smccc_1_1_invoke()
anyways, so I don't have any opinion against using unsigned long here...


PS. I understand why func_id is u32, but why are param_page and
param_offset u32?

Regards,
Bjorn