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 14:56:51 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Esben Haabendal <esben@...bendal.dk>
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

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?

> > 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?  :)

thanks,

greg k-h