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Date: Wed, 22 May 2002 12:41:16 +0400
From: Nick Kurshev <nickols_k@mail.ru>
To: linux-kernel@vger.kernel.org
Subject: /dev/port BUG and possible workaround
Message-Id: <20020522124116.680f59b8.nickols_k@mail.ru>
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Hello!

It seems that I've found out bug in subj
(sorry if this subj was already discussed here)

looking at sources of drivers/char/mem.c I found out:

static ssize_t read_port(struct file * file, char * buf,
			 size_t count, loff_t *ppos)
{
	unsigned long i = *ppos;
[snip]
	while (count-- > 0 && i < 65536) {
		if (__put_user(inb(i),tmp) < 0) 
			return -EFAULT;  
[snip]
}

static ssize_t write_port(struct file * file, const char * buf,
			  size_t count, loff_t *ppos)
{
	unsigned long i = *ppos;
[snip]
	while (count-- > 0 && i < 65536) {
		char c;
		if (__get_user(c, tmp)) 
			return -EFAULT; 
		outb(c,i);
[snip]
}

Well, when I'm trying to use this device in the way:
  lseek(port_fd,port_idx,SEEK_SET);
  write(port_fd,&val32,4);
I get perfectly broken results due outl() != outb()*4
Please look at logs:
1. Correct log with using of inport/outport:
outb(CF8,0)
outb(CFA,0)
FF=inb(CF8)
FF=inb(CFA)
80FFFFFC=inl(CF8)
outl(CF8,80000000)
80000000=inl(CF8)
outl(CF8,80FFFFFC)
outl(CF8,80000000)
3051106=inl(CFC)
outl(CF8,80000004)
22100006=inl(CFC)
outl(CF8,80000008)
6000003=inl(CFC)
outl(CF8,8000000C)
800=inl(CFC)
2. Wrong log with using of /dev/port:
outb(CF8,0)
outb(CFA,0)
FF=inb(CF8)
FF=inb(CFA)
FFFFFFFF=inl(CF8)
outl(CF8,80000000)
FFFFFFFF=inl(CF8)
outl(CF8,FFFFFFFF)

As possible workaround it would be better to examine size of
buffer and use corresponded insn within of these functions:
switch(size)
{
case 4: outl
case 2: outw
default: outb
}

But it seems that nobody uses this device. Then what is goal
of implementing of this device?

Best regards! Nick

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