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From: khalasa@piap.pl (Krzysztof Hałasa)
To: Arnd Bergmann <arnd@arndb.de>
Cc: Jason Cooper <jason@lakedaemon.net>,
	Marc Zyngier <marc.zyngier@arm.com>,
	Linus Walleij <linus.walleij@linaro.org>,
	Olof Johansson <olof@lixom.net>,
	Thomas Gleixner <tglx@linutronix.de>,
	Imre Kaloz <kaloz@openwrt.org>,
	Tim Harvey <tharvey@gateworks.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH 04/17 v1] irqchip: Add driver for IXP4xx
Date: Tue, 19 Feb 2019 07:51:05 +0100
Message-ID: <m37edwuv8m.fsf@t19.piap.pl> (raw)
In-Reply-To: <CAK8P3a0iubKdPrTO9ZxM+=0c3H8djpBw11KY-SO0Ai1Zgx3zHg@mail.gmail.com> (Arnd Bergmann's message of "Mon, 18 Feb 2019 13:44:19 +0100")

Arnd Bergmann <arnd@arndb.de> writes:

> - I have a vague memory that only specific revisions actually require
>   the PCI indirect mode. Is it the same chip revision A0 of IXP425
>   that requires both pci-indirect and address-coherent mode, or are
>   there other combinations?

IIRC, all chips support indirect PCI. Perhaps there are some changes
about LE mode on the PCI, but that's it.

Most boards don't need indirect PCI. It's only needed when there is more
than 64 MB of PCI address space to be used - IIRC IXP4xx have 4 direct
PCI memory access windows, and each is 16 MB in size.
I remember I needed indirect PCI for use with a (SiS?) VGA card, it had
(I guess) 128 MB of RAM. I think indirect PCI means the memory can't be
really mapped, it can only be accessed using readl() and friends (which
are then converted into register accesses resulting in the actual MMIO).
Even with indirect PCI, 64 MB can be accessed directly (though I think
we don't support it).

This is different from the bus mastering access to the main RAM - I
think only the first 64 MB can be used for PCI BM DMA. This limitation,
IIRC, doesn't apply to internal devices (Ethernet etc).

> - How much would it hurt actual users to drop support for both
>   features? I.e. do we know of anyone using the affected chips
>   (and still doing updates), or are the remaining ixp4xx systems
>   generally using the later chip revision?

Most chips are B0+, though there are (were) certain A0 platforms.
I don't have any idea about their current use.
-- 
Krzysztof Halasa

Industrial Research Institute for Automation and Measurements PIAP
Al. Jerozolimskie 202, 02-486 Warsaw, Poland

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Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-03 21:41 [PATCH 00/17 v1] ARM: ixp4xx: Modernize and DT support Linus Walleij
2019-02-03 21:41 ` [PATCH 01/17 v1] ARM: ixp4xx: Convert to MULTI_IRQ_HANDLER Linus Walleij
2019-02-03 21:41 ` [PATCH 02/17 v1] ARM: ixp4xx: Pass IRQ resource to beeper Linus Walleij
2019-02-03 21:41 ` [PATCH 03/17 v1] ARM: ixp4xx: Convert to SPARSE_IRQ Linus Walleij
2019-02-03 21:41 ` [PATCH 04/17 v1] irqchip: Add driver for IXP4xx Linus Walleij
2019-02-11 15:30   ` Marc Zyngier
2019-02-11 20:58     ` Linus Walleij
2019-02-11 22:11       ` Marc Zyngier
2019-02-18  7:06         ` khalasa
2019-02-18  7:16           ` Linus Walleij
2019-02-18  7:35             ` khalasa
2019-02-18  9:40             ` Arnd Bergmann
2019-02-18 12:03               ` khalasa
2019-02-18 12:44                 ` Arnd Bergmann
2019-02-19  6:51                   ` khalasa [this message]
2019-02-19  9:46                     ` Arnd Bergmann
2019-02-20  7:35                       ` khalasa
2019-02-18  9:18         ` Arnd Bergmann
2019-02-03 21:41 ` [PATCH 05/17 v1] gpio: ixp4xx: Add driver for the IXP4xx GPIO Linus Walleij
2019-02-06 16:03   ` Bartosz Golaszewski
2019-02-21  8:50     ` Linus Walleij
2019-02-03 21:41 ` [PATCH 06/17 v1] ARM: ixp4xx: Switch to use new IRQ+GPIO drivers Linus Walleij
2019-02-03 21:41 ` [PATCH 07/17 v1] clocksource/drivers/ixp4xx: Add driver Linus Walleij
2019-02-03 21:41 ` [PATCH 08/17 v1] ARM: ixp4xx: Switch to use new timer driver Linus Walleij
2019-02-03 21:41 ` [PATCH 09/17 v1] irqchip: ixp4xx: Add DT bindings Linus Walleij
2019-02-18 21:25   ` Rob Herring
2019-02-03 21:41 ` [PATCH 10/17 v1] irqchip: ixp4xx: Add OF initialization support Linus Walleij
2019-02-03 21:41 ` [PATCH 11/17 v1] clocksource/drivers/ixp4xx: Add DT bindings Linus Walleij
2019-02-18 21:26   ` Rob Herring
2019-02-18 22:10     ` Daniel Lezcano
2019-02-03 21:42 ` [PATCH 12/17 v1] clocksource/drivers/ixp4xx: Add OF initialization support Linus Walleij
2019-02-11 11:26   ` Daniel Lezcano
2019-02-03 21:42 ` [PATCH 13/17 v1] gpio: ixp4xx: Add DT bindings Linus Walleij
2019-02-06 16:05   ` Bartosz Golaszewski
2019-02-18 21:27   ` Rob Herring
2019-02-03 21:42 ` [PATCH 14/17 v1] gpio: ixp4xx: Add OF probing support Linus Walleij
2019-02-06 16:13   ` Bartosz Golaszewski
2019-02-21  8:55     ` Linus Walleij
2019-02-03 21:42 ` [PATCH 15/17 v1] ARM: ixp4xx: Add DT bindings Linus Walleij
2019-02-04 15:16   ` Rob Herring
2019-02-08 19:37     ` Linus Walleij
2019-02-03 21:42 ` [PATCH 16/17 v1] ARM: ixp4xx: Add device tree boot support Linus Walleij
2019-02-03 21:42 ` [PATCH 17/17 v1] RFC: ARM: dts: Add some initial IXP4xx device trees Linus Walleij

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