(EXT) Re: [PATCH v2 1/1] arm64: dts: imx8qm: Add fsl, imx7ulp-lpuart compatible to lpuart

[Alexander Stein]

Am Montag, dem 22.11.2021 um 09:43 +0800 schrieb Shawn Guo:
> On Tue, Nov 16, 2021 at 01:58:14PM +0100, Alexander Stein wrote:
> > After commit b4b844930f27 ("tty: serial: fsl_lpuart: drop earlycon
> > entry
> > for i.MX8QXP") earlycon support was essentially removed from
> > imx8qm/imx8qxp due to missing compatible.
> > The commit message says "i.MX8QXP lpuart is compatible with
> > i.MX7ULP" so
> > adding a fallback compatible should be fine.
> > With this change earlycon is supported again on imx8qm/imx8qxp.
> > 
> > Signed-off-by: Alexander Stein <
> > alexander.stein at ew.tq-group.com
> > >
> > Reviewed-by: Peng Fan <
> > peng.fan at nxp.com
> > >
> > ---
> > Changes in v2:
> > * Fix typo in commit message: 'early' -> 'earlycon'
> > 
> >  arch/arm64/boot/dts/freescale/imx8qm-ss-dma.dtsi | 8 ++++----
> >  1 file changed, 4 insertions(+), 4 deletions(-)
> > 
> > diff --git a/arch/arm64/boot/dts/freescale/imx8qm-ss-dma.dtsi
> > b/arch/arm64/boot/dts/freescale/imx8qm-ss-dma.dtsi
> > index bbe5f5ecfb92..3486b99ab6eb 100644
> > --- a/arch/arm64/boot/dts/freescale/imx8qm-ss-dma.dtsi
> > +++ b/arch/arm64/boot/dts/freescale/imx8qm-ss-dma.dtsi
> > @@ -19,19 +19,19 @@ uart4_lpcg: clock-controller at 5a4a0000 {
> >  };
> >  
> >  &lpuart0 {
> > -	compatible = "fsl,imx8qm-lpuart", "fsl,imx8qxp-lpuart";
> > +	compatible = "fsl,imx8qm-lpuart", "fsl,imx8qxp-lpuart",
> > "fsl,imx7ulp-lpuart";
> 
> Then fsl,imx8qxp-lpuart should be dropped?

If you drop fsl,imx8qxp-lpuart in the compatible list, fsl_lpuart.c
needs a new lpuart_soc_data for imx8qm in order to work. "fsl,imx7ulp-
lpuart" is not enough for imx8qm, as (among other things) "baud" clk is
mising in imx7. IMHO there are 2 ways:

1st
Add both fsl,imx8qxp-lpuart and fsl,imx7ulp-lpuart to the compatible
list to get both regular serial support (fsl,imx8qxp-lpuart) as well as
earlycon (fsl,imx7ulp-lpuart). In this case the bindings need to get
fixed as well, see [1]

2nd
Remove fsl,imx8qxp-lpuart compatible for imx8qm. But in this case
everything done for imx8qxp in fsl_lpuart.c has to be duplicated.
fsl,imx7ulp-lpuart is still required for earlycon support.

If you want to get rid of fsl,imx7ulp-lpuart compatible for
imx8qm/imx8qxp in either case, you need to revert b4b844930f27 ("tty:
serial: fsl_lpuart: drop earlycon entry for i.MX8QXP").

Best regards,
Alexander

[1] 
http://lists.infradead.org/pipermail/linux-arm-kernel/2021-November/697507.html