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

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Date:   Fri, 23 Feb 2018 11:02:01 +0000
From:   John Garry <john.garry@...wei.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.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 23/02/2018 10:30, Andy Shevchenko wrote:
> On Fri, 2018-02-23 at 02:42 +0800, John Garry wrote:
>> There is a requirement
>

Hi Andy,

> Where?
>

We require it for a development board for our hip06 platform. FWIW, 
here's a link to a board overview (does not mention UART particulars):
http://open-estuary.org/d03/

It uses the BMC virtual uart (16550A) over the LPC as the system UART. 
You know about the Hisi LPC support from here:
https://lkml.org/lkml/2018/2/19/460

>>  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.

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

>
>> - 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.

>> With patch 2/2, we're relaxing the interrupt support requirement.
>> As I mentioned in the commit log, the 8250_of.c driver seems to
>> ignore the dt bindings, and I do the same.
>
>

Thanks,
John