Hi Shimoda-san,
On Thu, Jan 26, 2023 at 1:55 AM Yoshihiro Shimoda
<yoshihiro.shimoda.uh@xxxxxxxxxxx> wrote:
> > From: Geert Uytterhoeven, Sent: Wednesday, January 25, 2023 5:55 PM
> > On Wed, Jan 25, 2023 at 1:49 AM Yoshihiro Shimoda
> > <yoshihiro.shimoda.uh@xxxxxxxxxxx> wrote:
> > > > From: Geert Uytterhoeven, Sent: Tuesday, January 24, 2023 11:35 PM
> > > > On Mon, Jan 23, 2023 at 2:35 AM Yoshihiro Shimoda
> > > > <yoshihiro.shimoda.uh@xxxxxxxxxxx> wrote:
> > > > > Since R-Car Gen4 doens't have the main IPMMU IMSSTR register, but
> > > > > each cache IPMMU has own module id. So, update descriptions of
> > > > > renesas,ipmmu-main property for R-Car Gen4.
> > > > >
> > > > > Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx>
> >
> > > > > ---
> > > > > The old R-Car S4-8 datasheet had described IPMMU IMSSTR register, but
> > > > > the latest datasheet undocumented the register. So, update the propeties
> > > > > description. Note that the second argument is not used on the driver.
> > > >
> > > > DT describes hardware, not software policy.
> > >
> > > I think so.
> > >
> > > > > So no behavior change.
> > > >
> > > > So where do we get the module id numbers to use, if they are no longer
> > > > documented in the Hardware Manual?
> > >
> > > If so, we cannot get the module id numbers. So, should we use other
> > > information which is completely fixed instead? I have some ideas:
> > > 1) Just 0 (or other fixed value) if the IMSSTR register doesn't exist.
> > > 2) Sequential numbers from register base offset.
> > > In R-Car S4: ipmmu_rt0 is the first node from register base offset,
> > > and ipmmu_rt1 is the second one.
> > > So, ipmmu_rt0 is 0, ipmmu_rt1 is 1, ipmmu_ds0 is 2 and ipmmu_hc is 3.
> > > 3) Using base address upper 16-bits.
> > > In R-Car S4: ipmmu_rt0 is 0xee480000. So, the value is 0xee48.
> > >
> > > Perhaps, the option 1) is reasonable, I think. But, what do you think?
> >
> > I would not make up numbers, as that would cause confusion with SoCs
> > where the numbers do match the hardware.
>
> I see.
>
> > As the driver doesn't use the module id number (it already loops
> > over all domains, instead of checking IMSSTR, probably because of
> > historical (R-Car Gen2) reasons?), what about dropping it from the
> > property? I.e. add "minItems: 1", possibly only when compatible with
> > renesas,rcar-gen4-ipmmu-vmsa?
>
> It looks a good idea to me.
>
> > BTW, the related IMCTR register is still documented, and the driver
> > does enable the interrupt bit (IMCTR_INTEN), so I'm wondering how the
> > hardware (documentation) people intend this to be used...
> > Perhaps IMCTR_INTEN will be removed/undocumented, too?
> > Or perhaps the removal/undocumentation of IMSSTR was a mistake?
>
> I don't think that IMCTR_INTEN will be removed/undocumented too because
> the IMCTR register is related to IMSTR register, not IMSSTR register ;)
> ~~~~~ ~~~~~~
> About undocumentation of IMSSTR, I found that accessing the register is
> possible to cause a potential issue on both R-Car Gen3/4. That's why
> the IMSSTR register is undocumented on R-Car Gen4. I'm not sure whether
> R-Car Gen3 will be undocumented too in the future though, but at least,
> we should not access the IMSSTR register on both R-Car Gen3/Gen4.
> # I'm not sure, but that's why the driver doesn't check IMSSTR to avoid
> # the potential issue??
IC
> So, to simplify the dt-bindings, just removing the second property without
> any condition is better, I think. But, what do you think?
So just add "minItems: 1", and leave out the second value of the
"renesas,ipmmu-main" property when adding support for new SoCs.
I don't think there is an immediate need to remove the existing second
value on already supported SoCs, as these values are not incorrect
hardware description.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
