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Fri, 8 Apr 2022 15:27:52 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C6C8FC385A1; Fri, 8 Apr 2022 15:27:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1649431672; bh=spbvvLexuDlNOPAlzsWxyFyJy2c3S3c/xnyxDLTAJKs=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=s3T+UM3bbC990eRqsi6NhvUT6CFbXbUzlJJ7VAxn07ZBhzQG+29cnyImFqJ3u727w pZEJ8O19sk/acW3gVNyv6AW5ROMaWOvbxBWslRzWb4LsTYFLl1A74/eY13LTuYBW0H LKbHb/t/fq6qI9uQDXerF3hB2GuwbykX3lAax31pCM380YN3KO75K9fkEul73+/cge 4IuvRaeP31LFPmQo1jOBvS2it/GgVn88HwAt40v24EBVYTRGoqdKWIuaJNAmFl7xXD mnUaCEJL6geLSL3bGHQbqjYjrB24GZZNBIhraFJa4bnwy5dhrBYDLMdZ6e9Yo/q3mv b17lE59IperfQ== Date: Fri, 8 Apr 2022 10:27:50 -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 v3 3/4] PCI: Add function for parsing 'slot-power-limit-milliwatt' DT property Message-ID: <20220408152750.GA306189@bhelgaas> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20220325093827.4983-4-pali@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org 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. 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; } ... 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. > +} > +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