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 E32C9C433EF for ; Fri, 25 Feb 2022 17:59:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231825AbiBYR7f (ORCPT ); Fri, 25 Feb 2022 12:59:35 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48642 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231504AbiBYR7b (ORCPT ); Fri, 25 Feb 2022 12:59:31 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EB6FA1C65CA; Fri, 25 Feb 2022 09:58:53 -0800 (PST) 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 A4FDFB832F8; Fri, 25 Feb 2022 17:58:52 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 06C71C340F0; Fri, 25 Feb 2022 17:58:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1645811931; bh=aqgDe5f2aVWTB6yqlpW2kcmFhzYgvTF+iOufv2e9koA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=uEnKDPmwYJntgyyIr8iVHCbSmFlv7ChMcb12YnGBy/QcSO4oQmowX/X8jfJbEcVcA rPWsAgAZXqKHaRTXunjnOKgPgdok9YmzWcWycNsB0ZwD7pGALx7OQEPFAkjlI/MxrP 1G90hFmiw2Lh4Jo15ZT8zHjIEfFn2EG1wmLwRLQEidJ6wYezydrnHwYldFUkyTnNgC oBHWFDFwlQq15eWQMF6oSvQnPSjmGXSS16PLWBTkRhdweQq2hOXGywPLEjlrpOvFbQ bAK8UDFTyzB4nBUskdGSth8/uIYlLc3KXFcRtX3z2okRmjpRHQeY4PwCH7359PphA+ bXSA1f49JXdEw== Received: by pali.im (Postfix) id 1CD487EF; Fri, 25 Feb 2022 18:58:48 +0100 (CET) Date: Fri, 25 Feb 2022 18:58:47 +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 , Gregory Clement , linux-pci@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 4/6] PCI: Add function for parsing 'slot-power-limit-milliwatt' DT property Message-ID: <20220225175847.gf6rvkamnyxjx2di@pali> References: <20220225123051.xlsv7fkesdf5upeh@pali> <20220225155156.GA358965@bhelgaas> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20220225155156.GA358965@bhelgaas> User-Agent: NeoMutt/20180716 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Friday 25 February 2022 09:51:56 Bjorn Helgaas wrote: > On Fri, Feb 25, 2022 at 01:30:51PM +0100, Pali Rohár wrote: > > On Thursday 24 February 2022 14:47:15 Bjorn Helgaas wrote: > > > On Tue, Feb 22, 2022 at 05:31:56PM +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 > > > > Acked-by: Bjorn Helgaas > > > > --- > > > > 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..2b0c0a3641a8 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; > > > > > > Including "mw" or similar reference to the units would give a hint of > > > how to relate the code to the spec. > > > > > > > + u8 value, scale; > > > > + > > > > + if (of_property_read_u32(node, "slot-power-limit-milliwatt", > > > > + &slot_power_limit)) > > > > + slot_power_limit = 0; > > > > + > > > > + /* Calculate Slot Power Limit Value and Slot Power Limit Scale */ > > > > > > Add a spec reference to PCIe r6.0, sec 7.5.3.9. IIUC, this supports > > > up to 300W, which was what r5.0 defined, but r6.0 added values up to > > > 0xfe (600W). > > > > I did not know about it and I have not seen/read r6.0. > > > > It would be nice if somebody with access to r6.0 send a patch to lspci > > utility, so we could write support for 600W based on lspci parser. > > Of course, sorry! Obviously you would have implemented them all if > you had the spec! > > Here's the info from r6.0, sec 7.5.3.9: > > Slot Power Limit Value - In combination with the Slot Power Limit > Scale value, specifies the upper limit on power supplied by the slot > (see § Section 6.9) or by other means to the adapter. > > Power limit (in Watts) is calculated by multiplying the value in > this field by the value in the Slot Power Limit Scale field except > when the Slot Power Limit Scale field equals 00b (1.0x) and Slot > Power Limit Value exceeds EFh, the following alternative encodings > are used: > > F0h > 239 W and ≤ 250 W Slot Power Limit > F1h > 250 W and ≤ 275 W Slot Power Limit > F2h > 275 W and ≤ 300 W Slot Power Limit > F3h > 300 W and ≤ 325 W Slot Power Limit > F4h > 325 W and ≤ 350 W Slot Power Limit > F5h > 350 W and ≤ 375 W Slot Power Limit > F6h > 375 W and ≤ 400 W Slot Power Limit > F7h > 400 W and ≤ 425 W Slot Power Limit > F8h > 425 W and ≤ 450 W Slot Power Limit > F9h > 450 W and ≤ 475 W Slot Power Limit > FAh > 475 W and ≤ 500 W Slot Power Limit > FBh > 500 W and ≤ 525 W Slot Power Limit > FCh > 525 W and ≤ 550 W Slot Power Limit > FDh > 550 W and ≤ 575 W Slot Power Limit > FEh > 575 W and ≤ 600 W Slot Power Limit > FFh Reserved for Slot Power Limit Values above 600 W > > This register must be implemented if the Slot Implemented bit is Set. > > Writes to this register also cause the Port to send the > Set_Slot_Power_Limit Message. Ok, thank you! I will send also update for lspci. > > > > + if (slot_power_limit == 0) { > > > > + value = 0x00; > > > > + scale = 0; > > > > + } else if (slot_power_limit <= 255) { > > > > + value = slot_power_limit; > > > > + scale = 3; > > > > + } else if (slot_power_limit <= 255*10) { > > > > + value = slot_power_limit / 10; > > > > + scale = 2; > > > > + } else if (slot_power_limit <= 255*100) { > > > > + value = slot_power_limit / 100; > > > > + scale = 1; > > > > + } else if (slot_power_limit <= 239*1000) { > > > > + value = slot_power_limit / 1000; > > > > + scale = 0; > > > > + } else if (slot_power_limit <= 250*1000) { > > > > + value = 0xF0; > > > > + scale = 0; > > > > + } else if (slot_power_limit <= 275*1000) { > > > > + value = 0xF1; > > > > + scale = 0; > > > > + } else { > > > > + value = 0xF2; > > > > + 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; > > > > > > If "slot-power-limit-milliwatt" contains a value larger than can be > > > represented in "value" and "scale", the return value will not agree > > > with value/scale, will it? > > > > In previous version 0xF2 was reserved for values above 275 W. So for me > > it looked like a correct solution. > > > > > Currently you only use the return value for a log message, so no real > > > harm yet, other than the fact that we might print "Slot power limit > > > 1000.0W" when the hardware will only advertise 600W available. > > > > > > Also, if "slot-power-limit-milliwatt" contains something like > > > 260000 mW (260 W), we'll return 0xF1/0, so the hardware will > > > advertise 275 W available. > > > > There is no way how to encode 260 W. It is possible only 250 W or 275 W, > > and nothing between. I chose to round value to upper limit. What do you > > prefer in these cases? Upper or lower limit? > > I think rounding down is better. If we round up, the slot will > advertise more power than it can deliver, and if the device tries to > consume the amount of power advertised, it may not work reliably. > > So I think we should return encoded values that are no higher than > what the slot can actually deliver, and the return value should match > what Slot Capabilities advertises. > > Bjorn It makes sense.