linux-kernel - RE: [PATCH 3/4] serial: 8250_dw: Add UPF_FIXED

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Date:	Thu, 23 Jul 2015 10:38:11 +0000
From:	Noam Camus <noamc@...hip.com>
To:	Peter Hurley <peter@...leysoftware.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	"Alexey.Brodkin@...opsys.com" <Alexey.Brodkin@...opsys.com>,
	"vgupta@...opsys.com" <vgupta@...opsys.com>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"jslaby@...e.com" <jslaby@...e.com>
Subject: RE: [PATCH 3/4] serial: 8250_dw: Add UPF_FIXED_TYPE to flags

From: Peter Hurley [mailto:peter@...leysoftware.com] 
Sent: Wednesday, July 22, 2015 3:39 PM

>> +	/* Writing to LCR may cause BUSY interrupt before we
>> +	 * register the IRQ line.
>> +	 * Currently autoconf() uses several writes to LCR.
>> +	 * In order to avoid calling to autoconf() always add
>> +	 * following flag.
>> +	 */
>> +	p->flags |= UPF_FIXED_TYPE; 
>
> Why only for devicetree DW8250's?  Don't all DW8250's have this LCR "feature"?
>
Yes, all DW8250 got this "feature" i.e. busy functionality.

> And what port type does this id DW8250's as, PORT_8250? Except with fifos, autoflow control, dma, etc.?
The only thing that DW8250 is not fully 16550 compatibility is this busy functionality feature.
This feature means that a serial transfer is in progress.
It is indicated by special identification in IIR, and raised when LCR is written while device is busy.

> If the port type is being fixed, then please fix it to a new port type.
As an extension to 16550 type is not fixed.

Seem that I need to rethink on this.
I will remove this commit from v2 patch set till I will be sure what is the right thing to do.

Noam