linux-kernel - Re: [PATCH 2/2] of: address: Preserve the flags portion on 1:1 dma-ranges mapping

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Message-ID: <ZzcoU8ckE7wXWC8w@apocalypse>
Date: Fri, 15 Nov 2024 11:54:11 +0100
From: Andrea della Porta <andrea.porta@...e.com>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Andrea della Porta <andrea.porta@...e.com>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...nel.org>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Florian Fainelli <florian.fainelli@...adcom.com>,
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczynski <kw@...ux.com>,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Bartosz Golaszewski <brgl@...ev.pl>,
	Derek Kiernan <derek.kiernan@....com>,
	Dragan Cvetic <dragan.cvetic@....com>,
	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Saravana Kannan <saravanak@...gle.com>, linux-clk@...r.kernel.org,
	devicetree@...r.kernel.org, linux-rpi-kernel@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, linux-gpio@...r.kernel.org,
	Masahiro Yamada <masahiroy@...nel.org>,
	Stefan Wahren <wahrenst@....net>,
	Herve Codina <herve.codina@...tlin.com>,
	Luca Ceresoli <luca.ceresoli@...tlin.com>,
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
	Andrew Lunn <andrew@...n.ch>, stable@...r.kernel.org
Subject: Re: [PATCH 2/2] of: address: Preserve the flags portion on 1:1
 dma-ranges mapping

Hi Bjorn,

On 10:56 Fri 08 Nov     , Bjorn Helgaas wrote:
> On Fri, Nov 08, 2024 at 11:39:21AM +0100, Andrea della Porta wrote:
> > A missing or empty dma-ranges in a DT node implies a 1:1 mapping for dma
> > translations. In this specific case, the current behaviour is to zero out
> > the entire specifier so that the translation could be carried on as an
> > offset from zero.  This includes address specifier that has flags (e.g.
> > PCI ranges).
> > Once the flags portion has been zeroed, the translation chain is broken
> > since the mapping functions will check the upcoming address specifier
> > against mismatching flags, always failing the 1:1 mapping and its entire
> > purpose of always succeeding.
> > Set to zero only the address portion while passing the flags through.
> 
> Add blank lines between paragraphs.

Ack.

> 
> > Fixes: dbbdee94734b ("of/address: Merge all of the bus translation code")
> > Cc: stable@...r.kernel.org
> > Signed-off-by: Andrea della Porta <andrea.porta@...e.com>
> > Tested-by: Herve Codina <herve.codina@...tlin.com>
> > ---
> >  drivers/of/address.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/of/address.c b/drivers/of/address.c
> > index 286f0c161e33..72b6accff21c 100644
> > --- a/drivers/of/address.c
> > +++ b/drivers/of/address.c
> > @@ -455,7 +455,8 @@ static int of_translate_one(struct device_node *parent, struct of_bus *bus,
> >  	}
> >  	if (ranges == NULL || rlen == 0) {
> >  		offset = of_read_number(addr, na);
> > -		memset(addr, 0, pna * 4);
> > +		/* copy the address while preserving the flags */
> 
> Not knowing the surrounding code, it seems strange to say "copy the
> address" when the memset() fills with zero and does no copying.
> 
> The commit log says "set address to zero, pass flags through," and I
> could believe *that* matches the memset().

Ack.

Many thanks,
Andrea

> 
> > +		memset(addr + pbus->flag_cells, 0, (pna - pbus->flag_cells) * 4);
> >  		pr_debug("empty ranges; 1:1 translation\n");
> >  		goto finish;
> >  	}
> > -- 
> > 2.35.3
> >