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

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Message-ID: <0dd9dc95-1329-0ad4-d03d-99899ea4f574@st.com>
Date:   Tue, 28 Jan 2020 16:41:29 +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>,
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        Loic PALLARDY <loic.pallardy@...com>,
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Subject: Re: [PATCH v2 2/7] bus: Introduce firewall controller framework


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.

I could argue that firewalls are not bus themselves they only interact 
with it.

Bus firewalls exist on other SoC, I hope some others could be added in 
this framework. ETZPC is only the first.

>
> 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

I have also tried to disable the nodes at runtime and Mark Rutland 
explain me why it was wrong.

Benjamin

>
> thanks,
>
> greg k-h