From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [Linaro-acpi] [RFC v2 1/3] Mailbox: Add support for ACPI Date: Mon, 23 Jun 2014 22:21:22 +0200 Message-ID: <14353430.fIAk0MDUYn@wuerfel> References: <1402591692-7736-1-git-send-email-ashwin.chaugule@linaro.org> <5338610.xCINKmsENX@wuerfel> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Return-path: Received: from mout.kundenserver.de ([212.227.126.187]:56643 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755079AbaFWUVd (ORCPT ); Mon, 23 Jun 2014 16:21:33 -0400 In-Reply-To: Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: linaro-acpi@lists.linaro.org Cc: Ashwin Chaugule , Patch Tracking , Jassi Brar , rjw@rjwysocki.net, linux-acpi@vger.kernel.org, Mark Brown , "linux-arm-kernel@lists.infradead.org" On Monday 23 June 2014 15:46:08 Ashwin Chaugule wrote: > Hello, > > On 23 June 2014 15:10, Arnd Bergmann wrote: > >> Fair point. The more I think about this, it seems that if we want to > >> use the mailbox framework for ACPI kernels, we should have a PCC > >> specific bypass, something like the one you suggested below. The ACPI > >> spec defines PCC as the only "mailbox" like mechanism. There are 3 PCC > >> clients defined as well; CPPC, MPST and RASF. Each of these have their > >> own ACPI tables and so they dont require special DSDT entries. > > > > Ok, I see. Can you describe what data is in these tables? > > For CPPC, its a field for version number, number of entries and then > followed by a bunch of PCC entries that have the following structure: > > 51 struct pcc_register_resource { > 52 u8 descriptor; > 53 u16 length; > 54 u8 space_id; > 55 u8 bit_width; > 56 u8 bit_offset; > 57 u8 access_size; > 58 u64 address; > 59 } __attribute__ ((packed)); > > These essentially describe the PCC register space to be used by the > respective protocol. e.g. CPPC uses these to exchange CPU performance > metrics between the OS and the firmware. > I believe MPST and RASF also follow the same format. Interesting. So I guess it's one entry per client of the PCC? How exactly does the client know which index to use in this table? Arnd