From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mirko Banchi Subject: Re: virtual -->physical --> virtual address Date: Sat, 15 Oct 2011 19:57:35 +0200 Message-ID: <891A5DF8-FC7F-4B14-9439-7123352847FB@gmail.com> References: Mime-Version: 1.0 (Apple Message framework v1084) Content-Transfer-Encoding: 8BIT Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=subject:mime-version:content-type:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to:x-pgp-agent :x-mailer; bh=AhiXAeDJsvgnUKeefToDBz7e4gj1VqrBiteRLo2lGc8=; b=vKzY616+01ME5yIRsiztyk1tpgFrNC5z99qHgcB+AnuutUq8u8G1dqQtZikust+yf6 Bx6xqVvUxNemCMu53IQXs1QY5P/rbCyRwtk9LUn+mfJORKoNm7KOKhH5UCkHna+9kjty gbIZSMefzdooMKwQ7q9mXvMa416Uyej0RgkT0= In-Reply-To: Sender: linux-modules-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" To: ratheesh kannoth Cc: linux-newbie , linux-c-programming-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-modules-u79uwXL29TY76Z2rM5mHXA@public.gmane.org -----BEGIN PGP SIGNED MESSAGE----- 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 id-jabber: mk.banchi-/eSpBmjxGS4dnm+yROfE0A@public.gmane.org PGP key fingerprint: 308F BFB1 4E67 2522 C88E DC69 7631 52ED 32A5 6456 -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (Darwin) iEYEARECAAYFAk6ZyZAACgkQdjFS7TKlZFaeIACfY5w9Z12jBkIUFvdreBPIQBcC CasAn1cAjnoWc/743741GREIDOa6zj9I =nkdk -----END PGP SIGNATURE-----