linux-kernel - Re: [PATCH 1/3] spi: spidev: fix the check for spidev in dt

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Date:	Sun, 26 Jun 2016 04:12:10 +0200
From:	Michal Suchanek <hramrach@...il.com>
To:	Mark Brown <broonie@...nel.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Dan Williams <dan.j.williams@...el.com>,
	Tejun Heo <tj@...nel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Davidlohr Bueso <dave@...olabs.net>,
	Andrey Ryabinin <aryabinin@...tuozzo.com>,
	Nikolay Aleksandrov <nikolay@...ulusnetworks.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Adrien Schildknecht <adrien+dev@...ischi.me>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-spi <linux-spi@...r.kernel.org>
Subject: Re: [PATCH 1/3] spi: spidev: fix the check for spidev in dt

On 26 June 2016 at 03:13, Mark Brown <broonie@...nel.org> wrote:
> On Thu, Jun 23, 2016 at 05:41:19PM -0000, Michal Suchanek wrote:
>
>> The check is supposed to warn about spidev specified directly in
>> devicetree as compatible. This just does not work. I have a devicetree
>> with no compatible whatsoever and hacked my kernel so I can manually
>> bind spidev. This still triggers.
>
> Well, a DT device won't instantiate without a compatible string...
> could you please explain exactly what makes you say this won't work?

That's because the whitelist concept for this check is completely broken.

Without any patches whatsoever I should be able to specify m25p80
binding in the DT, let the kernel create the device, unbind the
driver, and bind spidev.

Then I have the jedec,spi-nor compatible which is not on the whitelist.

>
>> Also I have no idea how this could have build with ! CONFIG_OF since the
>> id table which the code checks is not compiled then.
>
> of_match_device() compiles out when !OF.
>
>> +static const struct of_device_id spidev_check[] = {
>> +                     { .compatible = "spidev" },
>> +                     {}
>> +};
>
> The indentation here is completely non-standard.
>
>> -     if (spi->dev.of_node && !of_match_device(spidev_dt_ids, &spi->dev)) {
>> +     if (spi->dev.of_node && of_match_device(spidev_check, &spi->dev)) {
>
> I think what you intend to say in the commit message is that you want to
> change from a whitelist to a blacklist since that is what the code says,
> but like I say we also need an explanation of the logic behind such a
> change.

It's because the check kernel log message says it's a blacklist and
it's incorrectly implemented as a whitelist.

The change is to correct that.

Thanks

Michal