linux-kernel - Re: [RFC PATCH 0/2] serial: 8250_dw: IO space + polling mode support

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Message-ID: <1519407117.10722.124.camel@linux.intel.com>
Date:   Fri, 23 Feb 2018 19:31:57 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     John Garry <john.garry@...wei.com>, gregkh@...uxfoundation.org,
        jslaby@...e.com, p.zabel@...gutronix.de, heiko@...ech.de,
        ed.blake@...drel.com, jhogan@...nel.org
Cc:     linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        linuxarm@...wei.com
Subject: Re: [RFC PATCH 0/2] serial: 8250_dw: IO space + polling mode support

On Fri, 2018-02-23 at 11:02 +0000, John Garry wrote:
> On 23/02/2018 10:30, Andy Shevchenko wrote:
> > On Fri, 2018-02-23 at 02:42 +0800, John Garry wrote:
> > > There is a requirement
> 
> > Where?
> 
> We require it for a development board for our hip06 platform.

Okay, and this particular platform uses Synopsys IP?

> > >  for supporting an 8250-compatible UART with
> > > the following profile/features:
> > > - platform device
> > > - polling mode (i.e. no interrupt support)
> > > - ACPI FW
> > 
> > Elaborate this one, please.
> 
> So we need to define our own HID here, and cannot use PNP compatible
> CID 
> (like PNP0501) as we cannot use the 8250 PNP driver.

Why not? What are the impediments?

> This is related to the Hisi LPC ACPI support, where we would create
> an 
> MFD (i.e. platform device) for the UART.

Why you can't do properly in ACPI?

> > > - IO port iotype
> > > - 16550-compatible
> > > 
> > > For OF, we have 8250_of.c, and for PNP device we have 8250_pnp.c
> > > drivers. However there does not seem to any driver satisfying
> > > the above requirements. So this RFC is to find opinion on
> > > modifying the Synopsys DW 8250_dw.c driver to support these
> > > generic features.
> > 
> > Synopsys 8250 is a particular case of platform drivers. It doesn't
> > satisfy "8250-compatible UART" requirement.

> Right, but I wanted to try to use the generic parts of the driver to 
> support this UART to save writing yet another driver.

It's still odd. Why this one, why not 8250_foo_bar to touch instead?

-- 
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy