From: Mirko Banchi <mk.banchi-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
To: ratheesh kannoth <ratheesh.ksz-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Cc: linux-newbie
<linux-newbie-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
linux-c-programming-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
linux-modules-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: virtual -->physical --> virtual address
Date: Sat, 15 Oct 2011 19:57:35 +0200 [thread overview]
Message-ID: <891A5DF8-FC7F-4B14-9439-7123352847FB@gmail.com> (raw)
In-Reply-To: <CAGZFCEHW9Rpk8ZaFbaQPMeA_jOGFnFsnyqXg8QYJs+T+WpxpKw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
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Hash: SHA1
Il giorno 15/ott/2011, alle ore 09.01, ratheesh kannoth ha scritto:
> {
> virtual_addr1 = kmalloc(0x20, GFP_USER);
> phy_addr1 = __pa(virtual_addr1 );
> virtual_addr2 = ioremap(phy_addr1, 0x20 );
>
> }
>
>
> I noticed that virtual_addr1 is not equal to virtual_addr2. And if i
> dereference virtual_addr2 ( *virtual_addr2 ),
> kernel crash. What is wrong here ?
>
Obviously virtual_addr1 and virtual_addr2 are not equals! kmalloc returns a logical address (in fact you can simply calc the relative physical address with macro __pa) and ioremap returns a virtual address in the range [VMALLOC_START - VMALLOC_END]. However usually ioremap is used to deal with iomem and you shouldn't dereference the returned pointer directly: you should use instead ioread{8,16,32} or iowrite{8,16,32} family functions in order to make code portable. However i try to write a simple LKM with your code and i can dereference the pointer returned by ioremap correctly. Can you post some detailed code?
Mirko
- --
Mirko Banchi
e-mail: mk.banchi-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
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prev parent reply other threads:[~2011-10-15 17:57 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-10-15 7:01 virtual -->physical --> virtual address ratheesh kannoth
[not found] ` <CAGZFCEHW9Rpk8ZaFbaQPMeA_jOGFnFsnyqXg8QYJs+T+WpxpKw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2011-10-15 17:57 ` Mirko Banchi [this message]
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