linux-kernel - Re: [PATCH 00/21] On-demand device registration

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Date:	Thu, 11 Jun 2015 15:09:45 +0200
From:	Tomeu Vizoso <tomeu.vizoso@...labora.com>
To:	Alexander Holler <holler@...oftware.de>,
	Linus Walleij <linus.walleij@...aro.org>
CC:	Grant Likely <grant.likely@...aro.org>,
	Mark Rutland <mark.rutland@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>,
	"linux-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>,
	open@...dq.ahsoftware,
	"list@...dq.ahsoftware:DRM PANEL DRIVERS" 
	<dri-devel@...ts.freedesktop.org>, dmaengine@...r.kernel.org,
	Dan Williams <dan.j.williams@...el.com>,
	"linux-usb@...r.kernel.org" <linux-i2c@...r.kernel.org>
Subject: Re: [PATCH 00/21] On-demand device registration

On 06/11/2015 12:17 PM, Alexander Holler wrote:
> Am 11.06.2015 um 10:12 schrieb Linus Walleij:
>> On Wed, Jun 10, 2015 at 10:28 AM, Alexander Holler <holler@...oftware.de> wrote:
>>> Am 10.06.2015 um 09:30 schrieb Linus Walleij:
>>
>>>> i2c host comes out, probes the regulator driver, regulator driver
>>>> probes and then the regulator_get() call returns.
>>>>
>>>> This requires instrumentation on anything providing a resource
>>>> to another driver like those I mentioned and a lot of overhead
>>>> infrastructure, but I think it's the right approach. However I don't
>>>> know if I would ever be able to pull that off myself, I know talk
>>>> is cheap and I should show the code instead.
>>>
>>> You would end up with the same problem of deadlocks as currently, and you
>>> would still need something ugly like the defered probe brutforce to avoid
>>> them.
>>
>> Sorry I don't get that. Care to elaborate on why?
> 
> Because loading/initializing on demand doesn't give you any solved order 
> of drivers to initialize. And it can't because it has no idea about the 
> requirements of other drivers.

So, this is only about ordering device probing. All built-in drivers
have already registered themselves by when we start probing.

> The reason why it might work better in 
> the case of the tegra is that it might give you another initialization 
> order than the one which is currently choosen, which, by luck, might be 
> a better one.

Note that this series was also tested on iMX.6, Exynos and OMAP4.

> But maybe I missed something, I haven't looked at the patches at all. 

It's a really small patchset :)

  19 files changed, 130 insertions(+), 45 deletions(-)

Thanks,

Tomeu

> But just loading on demand, can't magically give you a working order of 
> drivers to initialize. E.g. how do you choose the first driver to 
> initialize?
> 
> Regards,
> 
> Alexander Holler
> 

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