linux-kernel - Re: [PATCH] of: property: fw_devlink: Add support for "mmc-pwrseq"

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Message-ID: <CAPDyKFqZsSi54FtYQR+vmjjUVmFPftipPdpUpDhCmEkTPiRH2w@mail.gmail.com>
Date: Mon, 12 Jan 2026 18:23:35 +0100
From: Ulf Hansson <ulf.hansson@...aro.org>
To: Sarav K <sarav.devel@...il.com>, Francesco Valla <francesco@...la.it>
Cc: Rob Herring <robh@...nel.org>, Saravana Kannan <saravanak@...nel.org>, linux-mmc@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] of: property: fw_devlink: Add support for "mmc-pwrseq"

On Mon, 12 Jan 2026 at 03:19, Sarav K <sarav.devel@...il.com> wrote:
>
> On Sat, Jan 10, 2026 at 7:28 AM Francesco Valla <francesco@...la.it> wrote:
> >
> > Add support for parsing MMC power sequencing (pwrseq) binding so that
> > fw_devlink can enforce the dependency.
> >
> > Signed-off-by: Francesco Valla <francesco@...la.it>
> > ---
> > Resending this patch as it slipped through the cracks (of my attention,
> > at least).
> >
> > Original submission is at [0]; there it appears as a v2 because it was
> > the first time I used b4. It was also part of [1], which wasn't really
> > a patchset but a follow-up to the boot time SIG meeting.
> >
> > I added Ulf and CC'd the mmc list, hoping they can (more
> > authoritatively than me) reply to Saravan's question:
> >
> > """
> > I took a quick look at the documentation. It's not clear to me that
> > mmc-pwrseq always points to a supplier. Can someone with more
> > experience on this confirm that is what it's supposed to point at?

Yes, the mmc-pwrseq property provides a phandle to the supplier.

> >
> > Meaning if A lists B as pwrseq, is it always the case that B needs to
> > be powered on? The binding documentation doesn't say anything about B
> > needs to be powered on first. It's just saying A and B have an
> > ordering requirement.

I assume with "powered on" you mean "probed". In that case, yes, A
(consumer) can't probe unless B (provider) has probed first.

Up until now, we have relied on deferred probing to manage this.

> >
> > If the meaning of the binding is _ALWAYS_ B needs to be powered on
> > first, then yes, this patch is correct and I can give a reviewed-by.
> > """
>
> Ulf, in case you missed it, this email is directed at you or other MMC folks.
>
> Francesco, can you see who added support for that property and direct
> your question specifically to them (in case it's not Ulf)?
>
> Is this fixing a specific issue for you that's pressing? If so, we can
> land  this and then see if anyone complains.

Thanks for pinging me about this. Please let me know if there is
anything unclear.

>
> Thanks,
> Saravana
>
> >
> > [0] https://lore.kernel.org/all/20250930-mmc_pwrseq-v2-1-80a8c6be0fb0@valla.it/
> > [1] https://lore.kernel.org/linux-embedded/20251126-beagleplay-probes-v1-0-c833defd4c9b@valla.it/T/
> >
> > Thank you!
> >
> > Regards,
> > Francesco
> > ---
> >  drivers/of/property.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/of/property.c b/drivers/of/property.c
> > index 4e3524227720a596b0f12976f83357851e9b94f3..05ae33a58b5aec0a8f4d3b7237ce88066d86dc9d 100644
> > --- a/drivers/of/property.c
> > +++ b/drivers/of/property.c
> > @@ -1410,6 +1410,7 @@ DEFINE_SIMPLE_PROP(post_init_providers, "post-init-providers", NULL)
> >  DEFINE_SIMPLE_PROP(access_controllers, "access-controllers", "#access-controller-cells")
> >  DEFINE_SIMPLE_PROP(pses, "pses", "#pse-cells")
> >  DEFINE_SIMPLE_PROP(power_supplies, "power-supplies", NULL)
> > +DEFINE_SIMPLE_PROP(mmc_pwrseq, "mmc-pwrseq", NULL)
> >  DEFINE_SUFFIX_PROP(regulators, "-supply", NULL)
> >  DEFINE_SUFFIX_PROP(gpio, "-gpio", "#gpio-cells")
> >
> > @@ -1557,6 +1558,7 @@ static const struct supplier_bindings of_supplier_bindings[] = {
> >         { .parse_prop = parse_msi_parent, },
> >         { .parse_prop = parse_pses, },
> >         { .parse_prop = parse_power_supplies, },
> > +       { .parse_prop = parse_mmc_pwrseq, },
> >         { .parse_prop = parse_gpio_compat, },
> >         { .parse_prop = parse_interrupts, },
> >         { .parse_prop = parse_interrupt_map, },
> >
> > ---
> > base-commit: b6151c4e60e5f695fac8b5c3e011cfcfd6e27cba
> > change-id: 20260110-mmc-pwrseq-e885e677ca2b
> >
> > Best regards,
> > --
> > Francesco Valla <francesco@...la.it>
> >

Kind regards
Uffe