linux-kernel - Re: [RFC][PATCH] axi: add AXI bus driver

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Date:	Wed, 13 Apr 2011 23:58:12 +0200
From:	Rafał Miłecki <zajec5@...il.com>
To:	George Kashperko <george@...u.edu.ua>
Cc:	Arend van Spriel <arend@...adcom.com>,
	"balbi@...com" <balbi@...com>,
	"linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
	"John W. Linville" <linville@...driver.com>,
	"b43-dev@...ts.infradead.org" <b43-dev@...ts.infradead.org>,
	Michael Büsch <mb@...sch.de>,
	Larry Finger <Larry.Finger@...inger.net>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Russell King <rmk@....linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>,
	Andy Botting <andy@...ybotting.com>,
	linuxdriverproject <devel@...uxdriverproject.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH] axi: add AXI bus driver

2011/4/13 Rafał Miłecki <zajec5@...il.com>:
> Will comment on that later.

Can we try to decide, how to implement our driver correctly? This
should be main focus for now. I tried to analyze drivers/amba/, how it
works, how it relates to our code, Broadcom.

AFAICS AMBA so far is mostly (always?) used for embedded devices with
pre-defined hardware layout. Let's take as example mach-u300 (just
some random one). One of the amba_devices it registers is uart0_device
which has two interesting fields:
.start = U300_UART0_BASE,
.end   = U300_UART0_BASE + SZ_4K - 1,
U300_UART0_BASE == (U300_SLOW_PER_PHYS_BASE+0x3000) == 0xc0013000
So this mach-u300 is well-specified device, every mach-u300 has uart0
at 0xc0013000.

It looks every AMBA device (like uart0) has some common fields, like:
u32 peripherialid0, peripherialid1, peripherialid2, peripherialid3;
u32 componentid0, componentid1, componentid2, componentid3;

I believe Broadcom's *agent* AKA *wrapper* is comparable to standard
amba device.

Of course agents/wrappers are not the same for every Broadcom AMBA AXI
card, so we can not use strict .start and .end declarations and the
same agents/wrappers for every card. Instead, we have to do scanning
of EPROM to read info about agents/wrappers.

If someone does not know: every core on Broadcom AMBA AXI card has
it's agent/wrapper. We access agent/wrapper registers to
enable/disable/reset core.

So we could scan EPROM for agents/wrappers, register them in AMBA
driver using our *_core_enable as AMBA's clock management.

Please verify if my understanding is correct. I tried to explain
easily whole situation I just analyzed.

If I'm right: is this really the right path to follow? What about real
core, like PCIe core, or IEEE core? I guess they are not standard AMBA
cores, so we can not simply register them. Should we look for clever
way to connect everything we have with drivers/amba? How to connect
"real" cores (PCIe, IEEE) with agents?

Please, share how do you see this situation now.

-- 
Rafał
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