linux-kernel - Re: [PATCH v3 5/5] tty/serial: Add Spreadtrum sc9836-uart driver support

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Message-ID: <7773522.25QE5ibXJZ@wuerfel>
Date:	Thu, 27 Nov 2014 16:36:52 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Lyra Zhang <zhang.lyra@...il.com>
Cc:	Murali Karicheri <m-karicheri2@...com>,
	Chunyan Zhang <chunyan.zhang@...eadtrum.com>,
	Grant Likely <grant.likely@...aro.org>,
	"robh+dt@...nel.org" <robh+dt@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
	"jslaby@...e.cz" <jslaby@...e.cz>,
	Kumar Gala <galak@...eaurora.org>,
	Mark Rutland <mark.rutland@....com>,
	Pawel Moll <pawel.moll@....com>,
	Ramkumar Ramachandra <artagnon@...il.com>,
	"rrichter@...ium.com" <rrichter@...ium.com>,
	Will Deacon <will.deacon@....com>,
	"gnomes@...rguk.ukuu.org.uk" <gnomes@...rguk.ukuu.org.uk>,
	Jonathan Corbet <corbet@....net>,
	"jason@...edaemon.net" <jason@...edaemon.net>,
	Mark Brown <broonie@...nel.org>,
	Heiko Stübner <heiko@...ech.de>,
	"florian.vaussard@...l.ch" <florian.vaussard@...l.ch>,
	"andrew@...n.ch" <andrew@...n.ch>,
	Hayato Suzuki <hytszk@...il.com>,
	Orson Zhai <orsonzhai@...il.com>,
	"geng.ren@...eadtrum.com" <geng.ren@...eadtrum.com>,
	"zhizhou.zhang" <zhizhou.zhang@...eadtrum.com>,
	"lanqing.liu@...eadtrum.com" <lanqing.liu@...eadtrum.com>,
	Wei Qiao (乔伟) <wei.qiao@...eadtrum.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"sprdlinux@...elists.org" <sprdlinux@...elists.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>
Subject: Re: [PATCH v3 5/5] tty/serial: Add Spreadtrum sc9836-uart driver support

On Thursday 27 November 2014 23:23:17 Lyra Zhang wrote:
> 
> Yes, I saw this way in other serial drivers.
> But, if then, there are two questions for me:
> 1. Why did some serial drivers need an UN_SHARED irq?

A lot of drivers were written before we had shared IRQs, or
were copied from old drivers, or are for hardware that uses
edge-triggered interrupts instead of level-triggered interrupts.

Only level-triggered interrupts can be shared.

> 2. How can we choose a right way?

It never hurts to implement a shared interrupt handler. Only
if you have no way to find out whether the device triggered
the interrupt or not you have to leave out IRQF_SHARED, and then
you won't be able to return IRQ_NONE.

	Arnd
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