linux-kernel - Re: [PATCH 2/2] serial: 8250: Add support for 8250/16550 as MFD function

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Date:   Tue, 21 May 2019 16:31:52 +0200
From:   Esben Haabendal <esben@...bendal.dk>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Lee Jones <lee.jones@...aro.org>, linux-serial@...r.kernel.org,
        Jiri Slaby <jslaby@...e.com>, Nishanth Menon <nm@...com>,
        Vignesh R <vigneshr@...com>, Tony Lindgren <tony@...mide.com>,
        Lokesh Vutla <lokeshvutla@...com>,
        Florian Fainelli <f.fainelli@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] serial: 8250: Add support for 8250/16550 as MFD function

Greg Kroah-Hartman <gregkh@...uxfoundation.org> writes:

> On Tue, May 21, 2019 at 01:50:25PM +0200, Esben Haabendal wrote:
>> Greg Kroah-Hartman <gregkh@...uxfoundation.org> writes:
>> 
>> > On Tue, May 21, 2019 at 01:11:08PM +0200, Esben Haabendal wrote:
>> >> Greg Kroah-Hartman <gregkh@...uxfoundation.org> writes:
>> >> 
>> >> >> I will try ad hold back with this thread until you get back to it.
>> >> >
>> >> > Ok, I have no idea what is going on here, sorry.  This is a really long
>> >> > and meandering thread, and I can't even find the original patches in my
>> >> > queue.
>> >> >
>> >> > So can you resend things and we can start over?  :)
>> >> 
>> >> Will do.
>> >> 
>> >> > But note, using a mfd for a uart seems VERY odd to me...
>> >> 
>> >> Ok.  In my case, I have a pcie card with an fpga which includes 5 uart
>> >> ports, 3 ethernet interfaces and a number of custom IP blocks.
>> >> I believe that an mfd driver for that pcie card in that case.
>> >
>> > I believe you need to fix that fpga to expose individual pci devices
>> > such that you can properly bind the individual devices to the expected
>> > drivers :)
>> 
>> Well, that is really out-of-scope of what I am doing here.
>
> Not really, if you have control over the fpga firmware (and odds are you
> do), just fix that and instantly your device works with all kernels, no
> need to change anything.
>
> Why not do this?

Because I do not have control over fpga firmware.

>> > Seriously, who makes such a broken fpga device that goes against the PCI
>> > spec that way?  Well, not so much as "goes against it", as "ignores all
>> > of the proper ideas of the past 20 years for working with PCI devices".
>> 
>> Might be.  But that is the firmware I have to work with here, and I
>> still hope we can find a good solution for implementing a driver without
>> having to maintain out-of-tree patches.
>
> As this hardware will not work on any operating system as-is, why not
> fix the firmware to keep from having to support a one-off device that no
> one else would be crazy enough to create?  :)

Clearly, someone has been crazy enough.  Hopefully, we can be smart
enough to make Linux fit to it.

/Esben