linux-kernel - Re: [RESEND v2] soc: imx: Add generic i.MX8 SoC driver

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Date:   Thu, 28 Mar 2019 16:43:55 +0000
From:   Leonard Crestez <leonard.crestez@....com>
To:     "l.stach@...gutronix.de" <l.stach@...gutronix.de>,
        Abel Vesa <abel.vesa@....com>,
        Anson Huang <anson.huang@....com>
CC:     dl-linux-imx <linux-imx@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Fabio Estevam <fabio.estevam@....com>, Ye Li <ye.li@....com>,
        "robh@...nel.org" <robh@...nel.org>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>
Subject: Re: [RESEND v2] soc: imx: Add generic i.MX8 SoC driver

On Fri, 2019-03-22 at 16:49 +0000, Abel Vesa wrote:
> Add generic i.MX8 SoC driver along with the i.MX8MQ SoC specific code.
> For now, only i.MX8MQ revision B1 is supported. For any other, i.MX8MQ
> revision it will print 'unknown'.

> +#define REV_B1				0x21
> +
> +#define IMX8MQ_SW_INFO_B1		0x40
> +#define IMX8MQ_SW_MAGIC_B1		0xff0055aa
> +
> +	np = of_find_compatible_node(NULL, NULL, "fsl,imx8mq-ocotp");+
> +	ocotp_base = of_iomap(np, 0);
> +
> +	magic = readl_relaxed(ocotp_base + IMX8MQ_SW_INFO_B1);
> +	if (magic == IMX8MQ_SW_MAGIC_B1)
> +		rev = REV_B1;

This is based on ATF code in vendor tree, but shouldn't we have some
sort of explanation for this "magic"?

Looking at the OCOTP driver reg 0x40 is IMX_OCOTP_ADDR_DATA2 and it's
used as part of fuse writes. According to the driver code 8mq is
compatible with 7d and this write path is enabled for imx8mq-ocotp. 

Looking at the OCOTP manual reg 0x40 is OCOTP_HW_OCOTP_READ_FUSE_DATA
and it's meant to be used together with IMX_OCOTP_ADDR_CTRL to read
info. Maybe my manual (rev0 2018-01) is incorrect?

Looking at the manual this will return the value of the fuse last
requested via IMX_OCOTP_ADDR_CTRL but no such request is made in this
driver. So reading from OCOTP 0x40 might return an unrelated value?!

The manual does document that fuse 0x440[3:0] is a "silicon revision
number"; maybe we should read that?

--
Regards,
Leonard