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

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Date:	Thu, 4 Jun 2015 17:40:58 +0200
From:	Michal Suchanek <hramrach@...il.com>
To:	Marek Vasut <marex@...x.de>
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>,
	MTD Maling List <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 4 June 2015 at 17:28, Marek Vasut <marex@...x.de> wrote:
> 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.

mtdinfo shows I have no mtd devices and the log shows that probe
failed unless I patch the kernel.

When there is *support* for of partitions the ofparser is run on mtd
probe. If it fails because it considers

>>         controller-data {
>>             samsung,spi-feedback-delay = <0>;
>>         };

an invalid partition and does not find any valid partition the probe fails.

There are two problems here

1) the above is not invalid. It just is not a partition. The parser
should not fail seeing this

2) the mtd probe should not fail when a partition parser fails and
should present the unpartitioned device

Both are addressed in separate patches.

Thanks

Michal
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