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 E75F3C433EF for ; Thu, 24 Mar 2022 17:13:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241088AbiCXRPR (ORCPT ); Thu, 24 Mar 2022 13:15:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34956 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1352161AbiCXRPO (ORCPT ); Thu, 24 Mar 2022 13:15:14 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1EDB6326F7; Thu, 24 Mar 2022 10:13:42 -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 ams.source.kernel.org (Postfix) with ESMTPS id BF3C5B82337; Thu, 24 Mar 2022 17:13:40 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 454AEC340EC; Thu, 24 Mar 2022 17:13:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1648142019; bh=jMi1G5nIwMEKhuPCL/A1QiK7aP2q19+GorUJGSunucs=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=Egwfe4rrC4QgezISl4qPVGP1OusolFa0RQbX4Ftdyx/XRCHIU/gAhzejII7unpM2o 6SjwZO/Zj797OyqbQg9m8TlsZaXvDgt4CBYY1jdURGssOABT/82RBUpBQiaGiozdI3 NZDZJnWw8iOpbT38ilwI9WmWXzwdLiJRVI9jTlLhjyncEtwLPI0xlSVqXN6wdqn6RO 8uHpM6PnvAZ1BvDbWVZjxoFhnRzbZwYe+hoau7pbIaQwedMuvm5ZosuJeuI/knQz7A NX+zWUaLfR98Kp312ZBhTx+Abn/UynAxReSJVacE/gXuAwoidrONNoi37xAER1mTfk U+celXAOvWMTw== Date: Thu, 24 Mar 2022 12:13:37 -0500 From: Bjorn Helgaas To: Pali =?iso-8859-1?Q?Roh=E1r?= Cc: Lorenzo Pieralisi , Bjorn Helgaas , Rob Herring , Andrew Lunn , Thomas Petazzoni , Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= , Marek =?iso-8859-1?Q?Beh=FAn?= , 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: <20220324171337.GA1458545@bhelgaas> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20220302145733.12606-4-pali@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org 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