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 83052C433F5 for ; Mon, 11 Apr 2022 11:15:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1343965AbiDKLRU (ORCPT ); Mon, 11 Apr 2022 07:17:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56092 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344023AbiDKLQb (ORCPT ); Mon, 11 Apr 2022 07:16:31 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 42D6D62EF; Mon, 11 Apr 2022 04:14:13 -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 D5FD9B81235; Mon, 11 Apr 2022 11:14:11 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 484C5C385A4; Mon, 11 Apr 2022 11:14:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1649675650; bh=FUDidj+yCQNkWNCiBLcbArSmTaPpfuHtOr8LouhWG+E=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=rSl639lb7udqT6DSX4cnfiDXPgbyFVOHMEgKSq9xuCbR961zFqwwIMBFzVz3U1yuu +p0Y/NsgAhPiiKanHNXCl0/pV7uvUQU42qI1Odgwj6YJERQRm7Y+27dHbFzHYkvrb5 EvyswOgvtitaIJV5gateSBfsZDh00lweKS2RKqCscnapvxbW4mzZY0JXzC8lOn7K60 A8R6hW9Tzw6DySBe3XqNdC31MN/CuX1PTJVZKmHYZwMJcvaWdQ4NjzlP5/wqzIvTqu HHw7UaV4eFJab/ISPsRgjs2jbA3TSrbtKsL9kKOQ0Hu+VQ+IYWwY+Dd8eRtOInHTey HMFAF1Y+1VkWw== Received: by pali.im (Postfix) id 22C70807; Mon, 11 Apr 2022 13:14:07 +0200 (CEST) Date: Mon, 11 Apr 2022 13:14:07 +0200 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 v3 3/4] PCI: Add function for parsing 'slot-power-limit-milliwatt' DT property Message-ID: <20220411111407.7ycuoldxjvqnkoo4@pali> References: <20220325093827.4983-4-pali@kernel.org> <20220408152750.GA306189@bhelgaas> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20220408152750.GA306189@bhelgaas> User-Agent: NeoMutt/20180716 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Friday 08 April 2022 10:27:50 Bjorn Helgaas wrote: > On Fri, Mar 25, 2022 at 10:38:26AM +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 v3: > > * Set 600 W when DT slot-power-limit-milliwatt > 600 W > > 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..5ebff26edd41 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; > > I think the spec is poorly worded here. PCIe r6.0, sec 7.5.3.9, says: > > F0h > 239 W and <= 250 W Slot Power Limit > > I don't think it's meaningful for the spec to include a range here. > The amount of power the slot can supply has a single maximum. I > suspect the *intent* of F0h/00b is that a device in the slot may > consume up to 250W. > > Your code above would mean that slot_power_limit_mw == 245,000 would > cause the slot to advertise F0h/00b (250W), which seems wrong. So for slot_power_limit_mw == 245 W we should set following values? slot_power_limit_mw = 239 W value = 0xF0 scale = 0 > I think we should do something like this instead: > > scale = 0; > if (slot_power_limit_mw >= 600*1000) { > value = 0xFE; > slot_power_limit_mw = 600*1000; > } else if (slot_power_limit_mw >= 575*1000) { > value = 0xFD; > slot_power_limit_mw = 575*1000; > } ... This is already implemented in branch: } else if (slot_power_limit_mw <= 600*1000) { value = 0xF0 + (slot_power_limit_mw / 1000 - 250) / 25; scale = 0; I will just add reducing of final slot_power_limit_mw value. > I raised an issue with the PCI SIG about this. > > > + } else if (slot_power_limit_mw <= 600*1000) { > > + value = 0xF0 + (slot_power_limit_mw / 1000 - 250) / 25; > > + scale = 0; > > + } else { > > + value = 0xFE; > > + scale = 0; > > + } > > + > > + if (slot_power_limit_value) > > + *slot_power_limit_value = value; > > + > > + if (slot_power_limit_scale) > > + *slot_power_limit_scale = scale; > > + > > + return slot_power_limit_mw; > > If the DT tells us 800W is available, we'll store (FEh/00b), which > means the slot can advertise to a downstream device that 600W is > available. I think that's correct, since the current spec doesn't > provide a way to encode any value larger than 600W. > > But the function still returns 800,000 mW, which means the next patch will > print: > > %s: Slot power limit 800.0W > > even though it programs Slot Capabilities to advertise 600W. > That's why I suggested setting slot_power_limit_mw = 600*1000 above. Ok, I will update slot_power_limit_mw value in next patch version. > > +} > > +EXPORT_SYMBOL_GPL(of_pci_get_slot_power_limit); > > diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h > > index 3d60cabde1a1..e10cdec6c56e 100644 > > --- a/drivers/pci/pci.h > > +++ b/drivers/pci/pci.h > > @@ -627,6 +627,9 @@ struct device_node; > > int of_pci_parse_bus_range(struct device_node *node, struct resource *res); > > int of_get_pci_domain_nr(struct device_node *node); > > int of_pci_get_max_link_speed(struct device_node *node); > > +u32 of_pci_get_slot_power_limit(struct device_node *node, > > + u8 *slot_power_limit_value, > > + u8 *slot_power_limit_scale); > > void pci_set_of_node(struct pci_dev *dev); > > void pci_release_of_node(struct pci_dev *dev); > > void pci_set_bus_of_node(struct pci_bus *bus); > > @@ -653,6 +656,18 @@ of_pci_get_max_link_speed(struct device_node *node) > > return -EINVAL; > > } > > > > +static inline u32 > > +of_pci_get_slot_power_limit(struct device_node *node, > > + u8 *slot_power_limit_value, > > + u8 *slot_power_limit_scale) > > +{ > > + if (slot_power_limit_value) > > + *slot_power_limit_value = 0; > > + if (slot_power_limit_scale) > > + *slot_power_limit_scale = 0; > > + return 0; > > +} > > + > > static inline void pci_set_of_node(struct pci_dev *dev) { } > > static inline void pci_release_of_node(struct pci_dev *dev) { } > > static inline void pci_set_bus_of_node(struct pci_bus *bus) { } > > -- > > 2.20.1 > > > > > > _______________________________________________ > > linux-arm-kernel mailing list > > linux-arm-kernel@lists.infradead.org > > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel