Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754245Ab0LAPCj (ORCPT ); Wed, 1 Dec 2010 10:02:39 -0500 Received: from mail-fx0-f46.google.com ([209.85.161.46]:56300 "EHLO mail-fx0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754065Ab0LAPCh (ORCPT ); Wed, 1 Dec 2010 10:02:37 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=googlemail.com; s=gamma; h=date:from:x-x-sender:to:cc:subject:in-reply-to:message-id :references:user-agent:mime-version:content-type; b=p9WPePBOA0r8sfR33NnktNSVLNqQ5UmnrHh22wGzB6a9tJimBeFfc1a+UKvFHfUQdR vcXlYmvMeJdoZuIaRSSfZpZtKtFwwxyYVlXRpRXnYxY2Td2xlcCjaP6Y9GkDUowMZdtq At2VsfaM+7wwc+83B+vL9gx4qGEXxZUtecsYE= Date: Wed, 1 Dec 2010 16:02:14 +0100 (CET) From: Hans Ulli Kroll X-X-Sender: elektroman@localhost.localdomain To: Paulius Zaleckas cc: Hans Ulli Kroll , Arnd Bergmann , linux-arm-kernel@lists.infradead.org, Russell King , linux-kernel@vger.kernel.org Subject: Re: [PATCH] ARM: Gemini: Add support for PCI BUS In-Reply-To: Message-ID: References: <1290860675-15453-1-git-send-email-ulli.kroll@googlemail.com> <201011291745.22566.arnd@arndb.de> <4CF3F687.6040801@gmail.com> <201011292102.41155.arnd@arndb.de> <4CF40AEF.7070200@gmail.com> User-Agent: Alpine 2.00 (LNX 1167 2008-08-23) MIME-Version: 1.0 Content-Type: MULTIPART/MIXED; BOUNDARY="8323328-400002316-1291215749=:8521" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7069 Lines: 176 This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. --8323328-400002316-1291215749=:8521 Content-Type: TEXT/PLAIN; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT On Wed, 1 Dec 2010, Paulius Zaleckas wrote: > On Wed, Dec 1, 2010 at 1:52 PM, Hans Ulli Kroll > wrote: > > > > > > On Tue, 30 Nov 2010, Paulius Zaleckas wrote: > > > >> On Tue, Nov 30, 2010 at 10:15 AM, Hans Ulli Kroll > >> wrote: > >> > > >> > > >> > On Mon, 29 Nov 2010, Paulius Zaleckas wrote: > >> > > >> >> On 11/29/2010 10:02 PM, Arnd Bergmann wrote: > >> >> > On Monday 29 November 2010 19:52:55 Paulius Zaleckas wrote: > >> >> > > On 11/29/2010 06:45 PM, Arnd Bergmann wrote: > >> >> > > > There are many differences between readl and __raw_readl, including > >> >> > > > > >> >> > > > * __raw_readl does not have barriers and does not serialize with > >> >> > > > ? ? spinlocks, so it breaks on out-of-order CPUs. > >> >> > > > * __raw_readl does not have a specific endianess, while readl is > >> >> > > > ? ? fixed little-endian, just as the hardware is in this case. > >> >> > > > ? ? The endian-conversion is a NOP on little-endian ARM, but required > >> >> > > > ? ? if you actually run on a big-endian ARM (you don't). > >> >> > > > * __raw_readl may not be atomic, gcc is free to split the access > >> >> > > > ? ? into byte wise reads (it normally does not, unless you mark > >> >> > > > ? ? the pointer __attribute__((packed))). > >> >> > > > > >> >> > > > In essence, it is almost never a good idea to use __raw_readl, and > >> >> > > > the double underscores should tell you so. > >> >> > > > >> >> > > You are wrong: > >> >> > > > >> >> > > Since CONFIG_ARM_DMA_MEM_BUFFERABLE is NOT defined for FA526 core, > >> >> > > no barriers are in use when using readl. It just translates into > >> >> > > le32_to_cpu(__raw_readl(x)). Now this CPU has physical pin for endianess > >> >> > > configuration and if you will chose big-endian you will fail to read > >> >> > > internal registers, because they ALSO change endianess and le32_to_cpu() > >> >> > > will screw it. However it is different when accessing registers through > >> >> > > PCI bus, then you need to use readl(). > >> >> > > >> >> > Ok, I only checked that the platform does not support big-endian Linux > >> >> > kernel, not if the HW designers screwed up their registers, sorry about > >> >> > that. > >> >> > > >> >> > The other points are of course still valid: If the code ever gets > >> >> > used on an out of order CPU, it is broken. More importantly, if someone > >> >> > looks at the code as an example for writing another PCI support code, > >> >> > it may end up getting copied to some place where it ends up causing > >> >> > trouble. > >> >> > > >> >> > The typical way to deal with mixed-endian hardware reliably is to have > >> >> > a header file containing code like > >> >> > > >> >> > #ifdef CONFIG_GEMINI_BIG_ENDIAN_IO > >> >> > #define gemini_readl(x) __swab32(readl(x)) > >> >> > #define ... > >> >> > #else > >> >> > #define gemini_readl(x) readl(x)) > >> >> > #endif > >> >> > > >> >> > This also takes care of the (not as unlikely as you'd hope) case that > >> >> > the next person reusing the PCI hardware wires its endianess different > >> >> > from the CPU endianess. > >> >> > >> >> Actually I am not very sure how CPU works in big endian mode :) > >> >> I have never tried it and I think only some guys who made it did that. > >> >> So readl will work for 99.99% of cases. In datasheet they say that: > >> >> "All registers in Gemini use Little Endian and must be accessed by aligned > >> >> 32-bit word operations. The bus connection interface logic provides an Endian > >> >> Conversion function." > >> >> For me it looks like it can mean whatever you want :) > >> >> > >> > > >> > I think the endianes pin switched only the cpu, not the hardware > >> > registers. > >> > >> Yes, but original driver used readl/writel and it does le32_to_cpu, > >> so that structure definition is just reversing it. > >> If you will use __raw_readl/__raw_writel than there will be no need > >> for this redefinition. > >> > >> > Here is some sample code from the ethernet devive on Gemini > >> > typedef union > >> > { > >> > ? ? ? ?unsigned int bits32; > >> > ? ? ? ?struct bit > >> > ? ? ? ?{ > >> > #if (BIG_ENDIAN==1) > >> > ? ? ? ? ? ? ? ?unsigned int reserved ? ? ? ? ? : 15; ? // bit 31:17 > >> > ? ? ? ? ? ? ? ?unsigned int v_bit_mode ? ? ? ? : 1; ? ?// bit 16 > >> > ? ? ? ? ? ? ? ?unsigned int device_id ? ? ? ? ?: 12; ? // bit 15:4 > >> > ? ? ? ? ? ? ? ?unsigned int revision_id ? ? ? ?: 4; ? ?// bit ?3:0 > >> > #else > >> > ? ? ? ? ? ? ? ?unsigned int revision_id ? ? ? ?: 4; ? ?// bit ?3:0 > >> > ? ? ? ? ? ? ? ?unsigned int device_id ? ? ? ? ?: 12; ? // bit 15:4 > >> > ? ? ? ? ? ? ? ?unsigned int v_bit_mode ? ? ? ? : 1; ? ?// bit 16 > >> > ? ? ? ? ? ? ? ?unsigned int reserved ? ? ? ? ? : 15; ? // bit 31:17 > >> > #endif > >> > >> The other thing is that this endianess redefinition is very starnge since > >> it should swap bytes and not bits inside this struct. So I assume that > >> big endian was never tested on this driver and it will not work. > >> But ofcouse I can be wrong here :) > >> > > > > At this momment my brain restarts in very slow motion mode ;-) > > This can't work. The definition Storlinksemi uses for swapping bits and > > bytes are totaly wrong. > > They never _even_ testet this, or understand little endian or big endian. > > Take this simple sample > > > > typedef union { > > ? ? ? ?unsigned int bits32; > > ? ? ? ?struct bit { > > #if (BIG_ENDIAN==0) > > ? ? ? ? ? ? ? ?unsigned int a ?: 1; > > ? ? ? ? ? ? ? ?unsigned int b ?: 31; > > #else > > ? ? ? ? ? ? ? ?unsigned int b ?: 31; > > ? ? ? ? ? ? ? ?unsigned int a ?: 1; > > #endif > > ? ? ? ?}; > > } TEST; > > > > They swaped the bits inside one byte > > Ha! Wait a minute. Looks like we are both wrong... > Read the beginning of: http://thread.gmane.org/gmane.linux.kernel/1037608 > > So it means we should use readl/writel and get rid of these non-portable > bit-fields... > get rid of _endianes_. Endianes is ordering of bytes (octets) in address space and _not_ bits in registers nor bytes. With the above example : a = 1; b = 0; you will get on little endian cpu this 0x01, 0x00, 0x00, 0x00 (0x00000001UL) in memory on big endian 0x00, 0x00, 0x00, 0x01 (0x01000000UL) _note_ the bits are not swapped, _only_ bytes. but if we use this _strange_ register layout with BIG_ENDIAN is set 0x00, 0x00, 0x00, 0x80 (0x80000000UL) I've done this _on_ paper to understand this. > >> > ? ? ? ?} bits; > >> > } TOE_VERSION_T; > >> > > >> > > >> > > >> > --8323328-400002316-1291215749=:8521-- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/