Re: [PATCH V3 0/9] arm64: imx8mn: Enable more imx8m Nano functions

[Lucas Stach]

Am Dienstag, dem 23.11.2021 um 08:08 -0600 schrieb Adam Ford:
> On Mon, Nov 22, 2021 at 3:52 PM Tim Harvey <tharvey@xxxxxxxxxxxxx> wrote:
> > 
> > On Mon, Nov 22, 2021 at 10:20 AM Lucas Stach <l.stach@xxxxxxxxxxxxxx> wrote:
> > > 
> > > Am Montag, dem 22.11.2021 um 09:59 -0800 schrieb Tim Harvey:
> > > > On Sun, Nov 21, 2021 at 7:25 AM Adam Ford <aford173@xxxxxxxxx> wrote:
> > > > > 
> > > > > On Sun, Nov 21, 2021 at 8:34 AM Adam Ford <aford173@xxxxxxxxx> wrote:
> > > > > > 
> > > > > > On Sun, Nov 21, 2021 at 8:21 AM Fabio Estevam <festevam@xxxxxxxxx> wrote:
> > > > > > > 
> > > > > > > Hi Adam,
> > > > > > > 
> > > > > > > On Sun, Nov 21, 2021 at 11:17 AM Adam Ford <aford173@xxxxxxxxx> wrote:
> > > > > > > 
> > > > > > > > I am using https://source.codeaurora.org/external/imx/imx-atf/log/?h=lf_v2.4
> > > > > > > > 
> > > > > > > > Since the driver sending SMCC commands to ATF isn't doing that, I
> > > > > > > > assume it's safe to use the linux power-domain drivers with the ATF
> > > > > > > > from NXP's kernel.
> > > > > > > > 
> > > > > > > > If you can point me to the repo you think I should be using, I'll give it a try.
> > > > > > > 
> > > > > > > Do you know if the mainline TF-A repo v2.5 works too?
> > > > > > > https://github.com/ARM-software/arm-trusted-firmware/tree/v2.5
> > > > > > 
> > > > > > That's good to know.
> > > > > > 
> > > > > > I just built it into U-Boot:
> > > > > > 
> > > > > > NOTICE:  BL31: v2.5(release):v2.5
> > > > > > NOTICE:  BL31: Built : 08:24:13, Nov 21 2021
> > > > > > 
> > > > > > The Etnaviv driver is still loading without hanging
> > > > > > 
> > > > > > root@beacon-imx8mn-kit:~# dmesg |grep -i etna
> > > > > > [   12.393936] etnaviv etnaviv: bound 38000000.gpu (ops gpu_ops [etnaviv])
> > > > > > [   12.400676] etnaviv-gpu 38000000.gpu: model: GC7000, revision: 6203
> > > > > > [   12.641297] [drm] Initialized etnaviv 1.3.0 20151214 for etnaviv on minor 0
> > > > > > 
> > > > > > 
> > > > > 
> > > > > Tim,
> > > > > 
> > > > > Which version of Nano do you have?  Not all Nano SoC's have a GPU from
> > > > > looking at the datasheet [1] .  I am using MIMX8MN2CVTIZAA (Nano Solo)
> > > > > 
> > > > > [1] - https://www.nxp.com/docs/en/data-sheet/IMX8MNIEC.pdf
> > > > > 
> > > > 
> > > > Adam,
> > > > 
> > > > The board I have here has MIMX8MN5CVTIZAA so i.MX 8M Nano QuadLite
> > > > with 'No GPU' as you expected.
> > > > 
> > > > So I have to add the following to keep my board from hanging after your series:
> > > > diff --git a/arch/arm64/boot/dts/freescale/imx8mn-venice-gw7902.dts
> > > > b/arch/arm64/boot/dts/freescale/imx8mn-venice-gw7902.dts
> > > > index 236f425e1570..0d256a607b7c 100644
> > > > --- a/arch/arm64/boot/dts/freescale/imx8mn-venice-gw7902.dts
> > > > +++ b/arch/arm64/boot/dts/freescale/imx8mn-venice-gw7902.dts
> > > > @@ -251,6 +251,10 @@
> > > >         };
> > > >  };
> > > > 
> > > > +&gpu {
> > > > +       status = "disabled";
> > > > +};
> > > > +
> > > >  &i2c1 {
> > > >         clock-frequency = <100000>;
> > > >         pinctrl-names = "default";
> > > > 
> > > > This situation is similar to the one I encountered with the
> > > > imx8mm-venice-gw7901 where adding the GPC node caused my board (which
> > > > did not power the GPU) to hang until I added disables to the
> > > > device-tree with commit 7973009235e2 ("arm64: dts:
> > > > imx8mm-venice-gw7901.dts: disable pgc_gpumix"). It feels painful to
> > > > have to add patches to keep things from hanging after additional
> > > > functionality is added to dt but perhaps that is more common than I
> > > > think esp for SoC's like IMX8M which have a lot of lingering support
> > > > still coming in.
> > > > 
> > > Yea, it's unfortunate that those patches break your board, but I guess
> > > we need to accept this, while there is still a lot of feature work
> > > going on.
> 
> There are a significant number of peripherals which are defined and
> marked as 'disabled' by default, so I don't think it's unreasonable to
> do that here.
> I'd like to propose we keep the default disabled and people who
> need/want the GPU enabled can turn it on.  Why waste the power if it's
> not needed?
> 
Sure, if a significant number of chips has the GPU disabled, we might
want to keep it disabled in the base dtsi. With those variants it's
always a tradeoff, for example there are SKUs of the i.MX6 that had the
VPU disabled, but very few of those were in the field, so the VPUs are
enabled in the SoC base dtsi and only users of those special SKUs would
need to disable them in the board DT.

The power argument isn't valid, as the kernel driver will suspend the
device when not needed, so there is no wasted power (aside from the
sort moment while the driver probes) with the GPU enabled.

The rule of thumb for when a device is default enabled in the SoC dsti
has always been (at least for i.MX) that the peripheral must not have a
board level dependency. While a i2c controller obviously needs a i2c
bus connected on the board to fulfill its purpose, a GPU can be used as
color space converter or something like that with no board level
interaction. Now the line is a bit blurred by having multiple power
rails into the SoC, so one could argue that the GPUs and VPUs now have
some board level dependency on the i.MX8M*.

Regards,
Lucas