From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 52485C433F5 for ; Fri, 25 Mar 2022 09:20:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1356681AbiCYJV5 (ORCPT ); Fri, 25 Mar 2022 05:21:57 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48384 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1356541AbiCYJVw (ORCPT ); Fri, 25 Mar 2022 05:21:52 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C81BBCF48C; Fri, 25 Mar 2022 02:20:18 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 60A0C60C33; Fri, 25 Mar 2022 09:20:18 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 69A01C340E9; Fri, 25 Mar 2022 09:20:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1648200017; bh=lxwHTABmCN1CazROEdpejwhPX+nwGGj7wnIuHcqcTZw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=TYxt8xCECLPqXVdNHCptJNzUFZzBhfTL09WONwZX7s/1yqG4DSTMEy03TGOAi7hxR T9IHLyZ1xPrudvbKDYUgxUZwJYqNqMTP5OJ2+2x7gsDmuTBp+pDKewmvcfIa4OyH51 I47vMRUd3fw/s971NUzdp0ccyT5ME8wMLWMfizeEGuI5GNZQn0zxbgAGgcjKNCXwRp nKUocdjQAz8SkrJwN2cCiLIrILerDZU46uDCBtMYOPf9utnR6ik8oBMpuknqxU5/mo zRP7IsSJKJT1kis4nzAJNHliEoVWuwu3XLrqWWYYjYmeXiKeIe/42ogv9gP+J+cgKO 5547Xbu3oJSfg== Received: by pali.im (Postfix) id 811B97DD; Fri, 25 Mar 2022 10:20:14 +0100 (CET) Date: Fri, 25 Mar 2022 10:20:14 +0100 From: Pali =?utf-8?B?Um9ow6Fy?= To: Bjorn Helgaas Cc: Lorenzo Pieralisi , Bjorn Helgaas , Rob Herring , Andrew Lunn , Thomas Petazzoni , Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= , Marek =?utf-8?B?QmVow7pu?= , Russell King , linux-pci@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 3/4] PCI: Add function for parsing 'slot-power-limit-milliwatt' DT property Message-ID: <20220325092014.yfxf474odzqfymml@pali> References: <20220302145733.12606-4-pali@kernel.org> <20220324171337.GA1458545@bhelgaas> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20220324171337.GA1458545@bhelgaas> User-Agent: NeoMutt/20180716 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thursday 24 March 2022 12:13:37 Bjorn Helgaas wrote: > On Wed, Mar 02, 2022 at 03:57:32PM +0100, Pali Rohár wrote: > > Add function of_pci_get_slot_power_limit(), which parses the > > 'slot-power-limit-milliwatt' DT property, returning the value in > > milliwatts and in format ready for the PCIe Slot Capabilities Register. > > > > Signed-off-by: Pali Rohár > > Signed-off-by: Marek Behún > > Reviewed-by: Rob Herring > > --- > > Changes in v2: > > * Added support for PCIe 6.0 slot power limit encodings > > * Round down slot power limit value > > --- > > drivers/pci/of.c | 64 +++++++++++++++++++++++++++++++++++++++++++++++ > > drivers/pci/pci.h | 15 +++++++++++ > > 2 files changed, 79 insertions(+) > > > > diff --git a/drivers/pci/of.c b/drivers/pci/of.c > > index cb2e8351c2cc..549a404bd536 100644 > > --- a/drivers/pci/of.c > > +++ b/drivers/pci/of.c > > @@ -633,3 +633,67 @@ int of_pci_get_max_link_speed(struct device_node *node) > > return max_link_speed; > > } > > EXPORT_SYMBOL_GPL(of_pci_get_max_link_speed); > > + > > +/** > > + * of_pci_get_slot_power_limit - Parses the "slot-power-limit-milliwatt" > > + * property. > > + * > > + * @node: device tree node with the slot power limit information > > + * @slot_power_limit_value: pointer where the value should be stored in PCIe > > + * Slot Capabilities Register format > > + * @slot_power_limit_scale: pointer where the scale should be stored in PCIe > > + * Slot Capabilities Register format > > + * > > + * Returns the slot power limit in milliwatts and if @slot_power_limit_value > > + * and @slot_power_limit_scale pointers are non-NULL, fills in the value and > > + * scale in format used by PCIe Slot Capabilities Register. > > + * > > + * If the property is not found or is invalid, returns 0. > > + */ > > +u32 of_pci_get_slot_power_limit(struct device_node *node, > > + u8 *slot_power_limit_value, > > + u8 *slot_power_limit_scale) > > +{ > > + u32 slot_power_limit_mw; > > + u8 value, scale; > > + > > + if (of_property_read_u32(node, "slot-power-limit-milliwatt", > > + &slot_power_limit_mw)) > > + slot_power_limit_mw = 0; > > + > > + /* Calculate Slot Power Limit Value and Slot Power Limit Scale */ > > + if (slot_power_limit_mw == 0) { > > + value = 0x00; > > + scale = 0; > > + } else if (slot_power_limit_mw <= 255) { > > + value = slot_power_limit_mw; > > + scale = 3; > > + } else if (slot_power_limit_mw <= 255*10) { > > + value = slot_power_limit_mw / 10; > > + scale = 2; > > + } else if (slot_power_limit_mw <= 255*100) { > > + value = slot_power_limit_mw / 100; > > + scale = 1; > > + } else if (slot_power_limit_mw <= 239*1000) { > > + value = slot_power_limit_mw / 1000; > > + scale = 0; > > + } else if (slot_power_limit_mw <= 250*1000) { > > + value = 0xF0; > > + scale = 0; > > + } else if (slot_power_limit_mw <= 600*1000) { > > + value = 0xF0 + (slot_power_limit_mw / 1000 - 250) / 25; > > + scale = 0; > > + } else { > > + value = 0xFF; > > + scale = 0; > > The purpose of this function is to return values that can be > programmed into the Slot Capabilities register. The 0xFF Slot Power > Limit Value is reserved, and I don't think we should use it until the > spec defines a meaning for it. > > If the DT tells us 800W is available, we'll put 0xFF in Slot Power > Limit Value. If the spec eventually defines (0xFF, 0) to mean "1000W > available", a device may try to consume all 1000W, which will not > work. > > If slot_power_limit_mw > 600*1000, I think we should advertise 600W > available (value 0xFE, scale 0) and return 600W (600*1000). > > Bjorn Ok, I will send a v3 with this change.