Re: [PATCH] ARM: imx: esdctl: fix LPDDR4 size calculation

[Lucas Stach <l.stach@pengutronix.de>]

Hi Teresa,

Am Freitag, dem 20.05.2022 um 14:16 +0000 schrieb Teresa Remmet:
> Hello Lucas,
> 
> Am Freitag, dem 13.05.2022 um 16:16 +0200 schrieb Lucas Stach:
> > The DDRC only uses the DEVICE_CONFIG field for memory types other
> > than
> > LPDDR4. While LPDDR4 always has a bus width of x32, the script aid
> 
> this is not true for i.MX8M Nano. This SoC has only x16. This is
> probably why reading the register worked for Joacim on imx8mn.
> So there is some more checking needed.
> 
Does the 8MN really use the DEVICE_CONFIG to configure the LPDDR4 bus
to 16bit width, or does it use the DATA_BUS_WIDTH control to limit the
bus to 16bit?

The register programming aid spreadsheet for the 8MN claims that
DEVICE_CONFIG has no effect on LPDDR4 memory, same as for all other
i.M8M* variants. But then the spreadsheet may have copy-and-paste
issues. So maybe we do in fact need to know that native bus width of
controller implementation on the specific SoC to get things right for
LPDDR4?

Regards,
Lucas

> Regards,
> Teresa
> 
> > generates the value for a x16 bus, as this was apparently used for
> > the
> > controller validation. This resulted in the calculated DRAM size to
> > be
> > halved on boards with LPDDR4 memory.
> > 
> > Fixes: d8d5778ee8c2 ("ARM: imx: Correct mem size calculation for
> > 4/8/16/32 bit bus width")
> > Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
> > ---
> >  arch/arm/mach-imx/esdctl.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/arch/arm/mach-imx/esdctl.c b/arch/arm/mach-imx/esdctl.c
> > index d3dbfff423da..4c8765c193d0 100644
> > --- a/arch/arm/mach-imx/esdctl.c
> > +++ b/arch/arm/mach-imx/esdctl.c
> > @@ -392,7 +392,7 @@ imx_ddrc_sdram_size(void __iomem *ddrc, const u32
> > addrmap[],
> >  	}
> >  
> >  	/* Bus width in bytes, 0 means half byte or 4-bit mode */
> > -	if (is_imx8)
> > +	if (is_imx8 && !(mstr & DDRC_MSTR_LPDDR4))
> >  		width = (1 << FIELD_GET(DDRC_MSTR_DEVICE_CONFIG, mstr))
> > > > 1;
> >  	else
> >  		width = 4;
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