From: Deepak Saxena <dsaxena@plexity.net>
To: Linus Torvalds <torvalds@osdl.org>
Cc: Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: Being more anal about iospace accesses..
Date: Wed, 15 Sep 2004 15:21:57 -0700 [thread overview]
Message-ID: <20040915222157.GA17284@plexity.net> (raw)
In-Reply-To: <Pine.LNX.4.58.0409150859100.2333@ppc970.osdl.org>
On Sep 15 2004, at 09:30, Linus Torvalds was caught saying:
> At the same time, we've had the proper "accessor" functions (read[bwl](),
> write[bwl]() and friends) that on purpose dropped all type information
> from the MMIO pointer, mostly just because of historical reasons, and as a
> result some drivers didn't use a pointer at all, but some kind of integer.
> Sometimes even one that couldn't _fit_ a MMIO address in it on a 64-bit
> machine.
Linus,
Since we are on the subject of io-access, I would like a
clarification/opinion on the read*/write* & in*/out* accessors
(and now the ioread/write equivalents). Are these functions only meant
to be used for PCI memory-mapped devices or _any_ memory mapped devices?
Same with ioremap(). I ask because there are bits of code in the
kernel that use these on non-PCI devices and this sometimes causes
some complication in platform-level code. For example, b/c of
the way PCI access work on the IXP4xx (indirect access via register
read/writes), we have to do the following to differentiate b/w
PCI and non-PCI devices (include/asm-arm/arch-ixp4xx/io.h):
static inline void *
__ixp4xx_ioremap(unsigned long addr, size_t size, unsigned long flags, unsigned long align)
{
extern void * __ioremap(unsigned long, size_t, unsigned long, unsigned long);
if((addr < 0x48000000) || (addr > 0x4fffffff))
return __ioremap(addr, size, flags, align);
return (void *)addr;
}
static inline void
__ixp4xx_writeb(u8 value, u32 addr)
{
u32 n, byte_enables, data;
if (addr >= VMALLOC_START) {
__raw_writeb(value, addr);
return;
}
n = addr % 4;
byte_enables = (0xf & ~BIT(n)) << IXP4XX_PCI_NP_CBE_BESL;
data = value << (8*n);
ixp4xx_pci_write(addr, byte_enables | NP_CMD_MEMWRITE, data);
}
#define writeb(p, v) __ixp4xx_writeb(p, v)
(0x48000000 -> 0x4fffffff is the PCI memory window on this CPU).
While this is not a huge level of uglyness, I have systems where
this is going to get much uglier b/c we have overlapping addresses
on different buses and we need to be able to differentiate accesses
It raises the question of whether we need a different interface
for non-PCI devices, if we should be passing a struct device into all
the I/O accessors functions to make it easier for platform code to
determine what to do, or if we should make I/O access functions a
property of devices. So instead of doing read*/write/in*/out*, we
would do either:
a) pass device into io-access routines:
cookie = iomap(dev, foo, len);
bar = read32(dev, cookie + offset);
or
b) make access routines a function of the devices themselves
cookie = dev->iomap(foo, len);
bar = dev->read32(cookie + REG_OFFSET);
The former is nicer b/c it allows the dev to be ignored on systems where
we do not care about PCI vs non-PCI devices.
Comments?
~Deepak
--
Deepak Saxena - dsaxena at plexity dot net - http://www.plexity.net/
"Unlike me, many of you have accepted the situation of your imprisonment
and will die here like rotten cabbages." - Number 6
next prev parent reply other threads:[~2004-09-15 22:25 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <Pine.LNX.4.58.0409081543320.5912@ppc970.osdl.org>
[not found] ` <Pine.LNX.4.58.0409150737260.2333@ppc970.osdl.org>
2004-09-15 16:30 ` Being more anal about iospace accesses Linus Torvalds
2004-09-15 16:54 ` Jörn Engel
2004-09-15 17:07 ` Linus Torvalds
2004-09-15 17:32 ` Jörn Engel
2004-09-15 17:57 ` Linus Torvalds
2004-09-15 18:06 ` Linus Torvalds
2004-09-15 19:34 ` Greg KH
2004-09-15 19:53 ` Linus Torvalds
2004-09-15 20:06 ` Greg KH
2004-09-16 14:58 ` Horst von Brand
2004-09-15 17:45 ` Nikita Danilov
2004-09-15 18:09 ` Linus Torvalds
2004-09-15 18:40 ` Chris Wedgwood
2004-09-15 17:07 ` Jeff Garzik
2004-09-15 17:16 ` Roland Dreier
2004-09-15 17:39 ` Linus Torvalds
2004-09-15 20:07 ` Russell King
2004-09-15 17:36 ` Horst von Brand
2004-09-15 17:40 ` Brian Gerst
2004-09-15 16:56 ` Dave Jones
2004-09-15 17:19 ` Roger Luethi
2004-09-15 17:23 ` Richard B. Johnson
2004-09-15 22:21 ` Deepak Saxena [this message]
2004-09-15 22:46 ` Linus Torvalds
2004-09-15 23:09 ` Deepak Saxena
2004-09-16 12:51 ` Geert Uytterhoeven
2004-09-16 22:10 ` Deepak Saxena
2004-09-15 22:29 ` Roland Dreier
2004-09-15 23:26 ` Being more careful " Linus Torvalds
2004-09-16 0:10 ` viro
2004-09-16 11:40 ` David Woodhouse
2004-09-16 12:25 ` David Woodhouse
2004-09-16 14:01 ` Linus Torvalds
2004-09-18 9:46 ` Kai Henningsen
2004-09-15 18:25 Being more anal " linux
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