linux-kernel - Re: [PATCH 04/11] mtd: ofpart: do not fail probe when no partitions exist

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Message-Id: <201506041728.50227.marex@denx.de>
Date:	Thu, 4 Jun 2015 17:28:50 +0200
From:	Marek Vasut <marex@...x.de>
To:	Michal Suchanek <hramrach@...il.com>
Cc:	Rob Herring <robh+dt@...nel.org>, Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Russell King <linux@....linux.org.uk>,
	Kukjin Kim <kgene@...nel.org>,
	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	Vinod Koul <vinod.koul@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Brian Norris <computersforpeace@...il.com>,
	Han Xu <han.xu@...escale.com>, Mark Brown <broonie@...nel.org>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	Rafał Miłecki <zajec5@...il.com>,
	Alison Chaiken <alison_chaiken@...tor.com>,
	Huang Shijie <b32955@...escale.com>,
	Ben Hutchings <ben@...adent.org.uk>,
	Knut Wohlrab <knut.wohlrab@...bosch.com>,
	"Bean Huo 霍斌斌 (beanhuo)" 
	<beanhuo@...ron.com>, "grmoore@...era.com" <grmoore@...era.com>,
	devicetree <devicetree@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-samsung-soc" <linux-samsung-soc@...r.kernel.org>,
	dmaengine <dmaengine@...r.kernel.org>,
	linux-mtd@...ts.infradead.org,
	"linux-spi" <linux-spi@...r.kernel.org>
Subject: Re: [PATCH 04/11] mtd: ofpart: do not fail probe when no partitions exist

On Thursday, June 04, 2015 at 06:54:00 AM, Michal Suchanek wrote:
> On 4 June 2015 at 00:58, Marek Vasut <marex@...x.de> wrote:
> > On Wednesday, June 03, 2015 at 11:26:40 PM, Michal Suchanek wrote:
> >> On Exynos it is necessary to set SPI controller parameters that apply to
> >> a SPI slave in a DT subnode of the slave device. The ofpart code returns
> >> an error when there are subnodes of the SPI flash but no partitions are
> >> found. Change this condition to a warning so that flash without
> >> partitions can be accessed on Exynos.
> > 
> > I have to admit the rationale for this patch is not very clear to me,
> > sorry. Can you please explain this a bit more ?
> 
> This is how the DT entry for SPI slave looks with s3c64xx:
> flash: m25p80@0 {
>         #address-cells = <1>;
>         #size-cells = <1>;
>         compatible = "jedec,spi-nor";
>         reg = <0>;
>         spi-max-frequency = <40000000>;
>         linux,max_tx_len = <65536>;

SIDENOTE: I thought this was actually added by your patch #8 in this
series. The underscores in the name of the property are not really
consistent with the rest of the names.

>         m25p,fast-read;
>         controller-data {
>             samsung,spi-feedback-delay = <0>;
>         };
>     };
> 
> this is example of flash partitions:
> flash@0 {
>         #address-cells = <1>;
>         #size-cells = <1>;
> 
>         partition@0 {
>                 label = "u-boot";
>                 reg = <0x0000000 0x100000>;
>                 read-only;
>         };
> 
>         uimage@...000 {
>                 reg = <0x0100000 0x200000>;
>         };
> };
> 
> The parser ignores any flash without subnodes and returns 0 (no
> partititon). When there is a subnode it assumes the flash is
> partitioned and tries to parse the subnodes as partitions. When there
> are subnodes and none parses as partition an error is returned. As
> shown above it is valid to have subnodes on unpartitioned flash.
>
> When an error is returned from a partition parser the mtdpart code
> passes on this error to the flash probe function and the proble of the
> flash fails.

What does /proc/mtd tell you when you have no partitions defined
in the DT ? It should provide you with the entire MTD device and
the code shouldn't even try to parse any OF partitions, since you
don't have any.

Best regards,
Marek Vasut
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