linux-kernel - Re: [PATCH v2 net-next 01/15] net: mdio-regmap: permit working with non-MMIO regmaps

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Message-ID: <aXMhWo0NpPK-BELG@smile.fi.intel.com>
Date: Fri, 23 Jan 2026 09:20:58 +0200
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Vladimir Oltean <vladimir.oltean@....com>
Cc: netdev@...r.kernel.org, Andrew Lunn <andrew@...n.ch>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	linux-kernel@...r.kernel.org,
	Herve Codina <herve.codina@...tlin.com>,
	Mark Brown <broonie@...nel.org>,
	Serge Semin <fancer.lancer@...il.com>,
	Maxime Chevallier <maxime.chevallier@...tlin.com>,
	Lee Jones <lee@...nel.org>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, devicetree@...r.kernel.org,
	Jiawen Wu <jiawenwu@...stnetic.com>
Subject: Re: [PATCH v2 net-next 01/15] net: mdio-regmap: permit working with
 non-MMIO regmaps

On Fri, Jan 23, 2026 at 12:18:48AM +0200, Vladimir Oltean wrote:
> On Thu, Jan 22, 2026 at 04:38:37PM +0200, Andy Shevchenko wrote:
> > On Thu, Jan 22, 2026 at 03:47:04PM +0200, Vladimir Oltean wrote:
> > > On Thu, Jan 22, 2026 at 02:13:01PM +0200, Vladimir Oltean wrote:

...

> > > > > > +	unsigned int base;
> > > > > 
> > > > > Hmm... resource_size_t ?
> > 
> > > > Well, regmap_read() takes "unsigned int reg".
> > > > https://elixir.bootlin.com/linux/v6.18.6/source/include/linux/regmap.h#L1297
> > > > So in practice, a truncation will be done somewhere if the register base
> > > > exceeds unsigned int storage capacity. But I didn't feel that it's worth
> > > > handling that.
> > > 
> > > Would this address your feedback?
> > 
> > Yes and no. See my remarks below.

...

> > > -	if (config->resource)
> > > +	if (config->resource) {
> > 
> > Btw, this might be not enough, one should check size and flags as well
> > before use. There was a discussion about this recently. Maybe we should
> > just move to a simple unsigned int in the config for now? Because handling
> > resources maybe considered as over engineering in this case.
> 
> The resource flags are never taken into consideration, but I can for
> sure replace the resource in struct mdio_regmap_config with just an
> unsigned int start and an end, but that doesn't get rid of the resource
> usage. The dev_get_resource(dev->parent, NULL) call is how we learn of
> where our register window is located in the "one big regmap" provided by
> the parent (SJA1105). So we still need this check somewhere else if we
> wanted to not fail silently in case of address bits truncation.

Hmm... Bu why we can't embed the full struct resource in such a case?
Because resource should have a flag check, otherwise it's a wrong check.

Discussion I mentioned is this:
https://lore.kernel.org/lkml/20251207215359.28895-1-ansuelsmth@gmail.com/

Fixes due to that finding:
https://lore.kernel.org/lkml/20251208200437.14199-1-ansuelsmth@gmail.com/
https://lore.kernel.org/lkml/20251208145654.5294-1-ilpo.jarvinen@linux.intel.com/

> > > +		if (config->resource->start > U32_MAX ||
> > > +		    config->resource->end > U32_MAX) {
> > 
> > Ideally it should be resource_overlaps() check. But see above.
> 
> resource_overlaps_with_what? The only problem is that the resource can
> exceed the 32 bit representation that regmap works with.

Obviously with the 4G address space :-)

	struct resource r4g = DEFINE_RESOURCE...(..., 0, SZ_4G...);

	if (resource_overlaps(&r4g, config->resource))
		aiaiai! // using %pR to print the content

> > > +			dev_err(config->parent,
> > > +				"Resource exceeds regmap API addressing possibilities\n");
> > > +			return ERR_PTR(-EINVAL);
> > > +		}
> > >  		mr->base = config->resource->start;
> > > +	}

-- 
With Best Regards,
Andy Shevchenko