linux-kernel - RE: [PATCH] soc: imx-scu: Add SoC UID(unique identifier) support

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Date:   Tue, 2 Jul 2019 07:23:16 +0000
From:   Anson Huang <anson.huang@....com>
To:     Marco Felsch <m.felsch@...gutronix.de>
CC:     Daniel Baluta <daniel.baluta@...il.com>,
        Aisheng Dong <aisheng.dong@....com>,
        Abel Vesa <abel.vesa@....com>, Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Daniel Baluta <daniel.baluta@....com>,
        dl-linux-imx <linux-imx@....com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: RE: [PATCH] soc: imx-scu: Add SoC UID(unique identifier) support

Hi, Marco

> Hi Anson,
> 
> On 19-06-27 07:01, Anson Huang wrote:
> > Hi, Daniel
> >
> > > On Thu, Jun 27, 2019 at 3:48 AM Anson Huang <anson.huang@....com>
> > > wrote:
> > > >
> > > > Hi, Daniel
> > > >
> > > > > On Wed, Jun 26, 2019 at 10:06 AM <Anson.Huang@....com> wrote:
> > > > > >
> > > > > > From: Anson Huang <Anson.Huang@....com>
> > > > > >
> > > > > > Add i.MX SCU SoC's UID(unique identifier) support, user can
> > > > > > read it from sysfs:
> > > > > >
> > > > > > root@...8qxpmek:~# cat /sys/devices/soc0/soc_uid
> > > > > > 7B64280B57AC1898
> > > > > >
> > > > > > Signed-off-by: Anson Huang <Anson.Huang@....com>
> > > > > > ---
> > > > > >  drivers/soc/imx/soc-imx-scu.c | 35
> > > > > > +++++++++++++++++++++++++++++++++++
> > > > > >  1 file changed, 35 insertions(+)
> > > > > >
> > > > > > diff --git a/drivers/soc/imx/soc-imx-scu.c
> > > > > > b/drivers/soc/imx/soc-imx-scu.c index 676f612..8d322a1 100644
> > > > > > --- a/drivers/soc/imx/soc-imx-scu.c
> > > > > > +++ b/drivers/soc/imx/soc-imx-scu.c
> > > > > > @@ -27,6 +27,36 @@ struct imx_sc_msg_misc_get_soc_id {
> > > > > >         } data;
> > > > > >  } __packed;
> > > > > >
> > > > > > +struct imx_sc_msg_misc_get_soc_uid {
> > > > > > +       struct imx_sc_rpc_msg hdr;
> > > > > > +       u32 uid_low;
> > > > > > +       u32 uid_high;
> > > > > > +} __packed;
> > > > > > +
> > > > > > +static ssize_t soc_uid_show(struct device *dev,
> > > > > > +                           struct device_attribute *attr,
> > > > > > +char
> > > > > > +*buf) {
> > > > > > +       struct imx_sc_msg_misc_get_soc_uid msg;
> > > > > > +       struct imx_sc_rpc_msg *hdr = &msg.hdr;
> > > > > > +       u64 soc_uid;
> > > > > > +
> > > > > > +       hdr->ver = IMX_SC_RPC_VERSION;
> > > > > > +       hdr->svc = IMX_SC_RPC_SVC_MISC;
> > > > > > +       hdr->func = IMX_SC_MISC_FUNC_UNIQUE_ID;
> > > > > > +       hdr->size = 1;
> > > > > > +
> > > > > > +       /* the return value of SCU FW is in correct, skip
> > > > > > + return value check */
> > > > >
> > > > > Why do you mean by "in correct"?
> > > >
> > > > I made a mistake, it should be "incorrect", the existing SCFW of
> > > > this API returns an error value even this API is successfully
> > > > called, to make it work with current SCFW, I have to skip the
> > > > return value check for this API for now. Will send V2 patch to fix this
> typo.
> > >
> > > Thanks Anson! It makes sense now. It is a little bit sad though
> > > because we won't know when there is a "real" error :).
> > >
> > > Lets update the comment to be more specific:
> > >
> > > /* SCFW FW API always returns an error even the function is
> > > successfully executed, so skip returned value */
> >
> > OK, as for external users, the SCFW formally released has this issue,
> > so for now I have to skip the return value check for this API, once
> > next SCFW release has this issue fixed, I will add a patch to check the return
> value.
> 
> Do you really keep track of that? Please can you add a FIXME: or TODO:
> tag and add the firmware version containing that bug?

Thanks for reminder, I just double checked the SCU FW code, it is actually a mistake, the SCU FW
API of sc_misc_unique_id() is actually a void function, which means it does NOT return anything.
While in our internal kernel tree, we make SCU IPC call to sc_misc_unique_id() with return value
check, and the return value is failure (-5) always. When I clean up the code for upstream, I did NOT notice it.
So the correct comment should be, this API does NOT return anything, no need to check the returned value.
I will fix the comment in next version.

void sc_misc_unique_id(sc_ipc_t ipc, uint32_t *id_l, uint32_t *id_h)

Thanks,
Anson

> 
> Regards,
>   Marco
> 
> > Thanks,
> > Anson.
> > >
> > >
> > > > > > +       imx_scu_call_rpc(soc_ipc_handle, &msg, true);
> > > > > > +
> > > > > > +       soc_uid = msg.uid_high;
> > > > > > +       soc_uid <<= 32;
> > > > > > +       soc_uid |= msg.uid_low;
> > > > > > +
> > > > > > +       return sprintf(buf, "%016llX\n", soc_uid);
> > > > >
> > > > > snprintf?
> > > >
> > > > The snprintf is to avoid buffer overflow, which in this case, I
> > > > don't know the size of "buf", and the value(u64) to be printed is
> > > > with fixed length of 64, so I think sprint is just OK.
> > >
> > > Ok.
> 
> --