linux-kernel - Re: [PATCH] ARM: dts: Add omap3-echo

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Date:   Wed, 25 Dec 2019 18:01:33 +0100
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Tony Lindgren <tony@...mide.com>
Cc:     André Hentschel <nerv@...ncrow.de>,
        webmaster@...ncrow.de, linux@....linux.org.uk, robh+dt@...nel.org,
        mark.rutland@....com, bcousson@...libre.com,
        linux-omap@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: dts: Add omap3-echo

Hi,

> Am 24.12.2019 um 19:45 schrieb Tony Lindgren <tony@...mide.com>:
> 
> * André Hentschel <nerv@...ncrow.de> [191224 16:11]:
>> This is the first generation Amazon Echo from 2016.
>> Audio support is not yet implemented.
> 
> OK looks good to me, just worried about one part:
> 
>> +&sgx_module {
>> +	status = "disabled";
>> +};
> 
> We should have a separate am3703.dtsi or whatever the SoC model
> disabling sgx if not there on the SoC.

I think the am3703 is a dm3730 (omap3630) where the SGX and the
DSP have not passed production test and are "disabled" by eFuses.
This is a common procedure in silicon production to increase yield.

Therefore, there is a register which allows to dynamically determine
what components (SGX and DSP) are available on a specific SoC chip.
See "Table 1-6. Chip Identification" in the common
"AM/DM37x Multimedia Device TRM".

Such bits exists for omap34xx and for omap36xx (aka am37xx/dm37xx).

That way there is no need to disable/enable sgx through device tree
variations and introducing more complexity by introducing more and more
DTS for variants (am3703.dtsi, am3715.dtsi, dm3720.dtsi, dm3730.dtsi?).

BTW: what about a board that is/was produced in either am3703 or dm3730
variants? Can they still share an omap36xx.dtsi based DTB?

So IMHO if there is an issue with sgx enabled on am3703 but no SGX
hardware available on a specific SoC, the sysc setup should somehow read
the bits and effectively disable all SGX related setup if it is not
available on the SoC. If I remember correctly, some older hwmods did
such things by checking SoC variant bits.

BR and thanks,
Nikolaus