linux-kernel - Re: [PATCH v2 2/7] bus: Introduce firewall controller framework

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Date:   Tue, 28 Jan 2020 20:29:45 +0000
From:   Benjamin GAIGNARD <benjamin.gaignard@...com>
To:     Greg KH <gregkh@...uxfoundation.org>
CC:     "broonie@...nel.org" <broonie@...nel.org>,
        "robh@...nel.org" <robh@...nel.org>,
        "arnd@...db.de" <arnd@...db.de>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "fabio.estevam@....com" <fabio.estevam@....com>,
        "sudeep.holla@....com" <sudeep.holla@....com>,
        "lkml@...ux.net" <lkml@...ux.net>,
        Loic PALLARDY <loic.pallardy@...com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-imx@....com" <linux-imx@....com>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
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        <system-dt@...ts.openampproject.org>,
        "stefano.stabellini@...inx.com" <stefano.stabellini@...inx.com>
Subject: Re: [PATCH v2 2/7] bus: Introduce firewall controller framework


On 1/28/20 5:57 PM, Greg KH wrote:
> On Tue, Jan 28, 2020 at 04:41:29PM +0000, Benjamin GAIGNARD wrote:
>> On 1/28/20 4:52 PM, Greg KH wrote:
>>> On Tue, Jan 28, 2020 at 04:38:01PM +0100, Benjamin Gaignard wrote:
>>>> The goal of this framework is to offer an interface for the
>>>> hardware blocks controlling bus accesses rights.
>>>>
>>>> Bus firewall controllers are typically used to control if a
>>>> hardware block can perform read or write operations on bus.
>>> So put this in the bus-specific code that controls the bus that these
>>> devices live on.  Why put it in the driver core when this is only on one
>>> "bus" (i.e. the catch-all-and-a-bag-of-chips platform bus)?
>> It is really similar to what pin controller does, configuring an
>> hardware block given DT information.
> Great, then use that instead :)
I think that Linus W. will complain if I do that :)
>
>> I could argue that firewalls are not bus themselves they only interact
>> with it.
> They live on a bus, and do so in bus-specific ways, right?
>
>> Bus firewalls exist on other SoC, I hope some others could be added in
>> this framework. ETZPC is only the first.
> Then put it on the bus it lives on, and the bus that the drivers for
> that device are being controlled with.  That sounds like the sane place
> to do so, right?

If that means that all drivers have to be modified it will be 
problematic because not all

are specifics to the SoC.

>
>>> And really, this should just be a totally new bus type, right?  And any
>>> devices on this bus should be changed to be on this new bus, and the
>>> drivers changed to support them, instead of trying to overload the
>>> platform bus with more stuff.
>> I have tried to use the bus notifier to avoid to add this code at probe
>> time but without success:
>>
>> https://lkml.org/lkml/2018/2/27/300
> Almost 2 years ago?  I can't remember something written 1 week ago...
>
> Yes, don't abuse the notifier chain.  I hate that thing as it is.
>
>> I have also tried to disable the nodes at runtime and Mark Rutland
>> explain me why it was wrong.
> The bus controller should do this, right?  Why not just do it there?

The bus controller is a different hardware block.


>
> thanks,
>
> greg k-h