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charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Mar 02, 2022 at 03:57:32PM +0100, Pali Roh=E1r 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 Roh=E1r > Signed-off-by: Marek Beh=FAn > 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 *no= de) > 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_v= alue > + * 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 =3D 0; > + > + /* Calculate Slot Power Limit Value and Slot Power Limit Scale */ > + if (slot_power_limit_mw =3D=3D 0) { > + value =3D 0x00; > + scale =3D 0; > + } else if (slot_power_limit_mw <=3D 255) { > + value =3D slot_power_limit_mw; > + scale =3D 3; > + } else if (slot_power_limit_mw <=3D 255*10) { > + value =3D slot_power_limit_mw / 10; > + scale =3D 2; > + } else if (slot_power_limit_mw <=3D 255*100) { > + value =3D slot_power_limit_mw / 100; > + scale =3D 1; > + } else if (slot_power_limit_mw <=3D 239*1000) { > + value =3D slot_power_limit_mw / 1000; > + scale =3D 0; > + } else if (slot_power_limit_mw <=3D 250*1000) { > + value =3D 0xF0; > + scale =3D 0; > + } else if (slot_power_limit_mw <=3D 600*1000) { > + value =3D 0xF0 + (slot_power_limit_mw / 1000 - 250) / 25; > + scale =3D 0; > + } else { > + value =3D 0xFF; > + scale =3D 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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel