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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 Mon, Apr 11, 2022 at 01:14:07PM +0200, Pali Roh=E1r wrote: > On Friday 08 April 2022 10:27:50 Bjorn Helgaas wrote: > > On Fri, Mar 25, 2022 at 10:38:26AM +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 Registe= r. > > > = > > > Signed-off-by: Pali Roh=E1r > > > Signed-off-by: Marek Beh=FAn > > > 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-milliw= att" > > > + * 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_lim= it_value > > > + * and @slot_power_limit_scale pointers are non-NULL, fills in the v= alue 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; > > = > > I think the spec is poorly worded here. PCIe r6.0, sec 7.5.3.9, says: > > = > > F0h > 239 W and <=3D 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 =3D=3D 245,000 would > > cause the slot to advertise F0h/00b (250W), which seems wrong. > = > So for slot_power_limit_mw =3D=3D 245 W we should set following values? > = > slot_power_limit_mw =3D 239 W > value =3D 0xF0 > scale =3D 0 I think Slot Cap should never advertise more power than the slot can supply. So if the DT tells us the slot can supply 245 W, I don't think Slot Cap should advertise that it can supply 250 W. I think we should drop down to the next lower possible value, which is 239 W (value 0xEF, scale 0). I think this is what your v4 does. > > I think we should do something like this instead: > > = > > scale =3D 0; > > if (slot_power_limit_mw >=3D 600*1000) { > > value =3D 0xFE; > > slot_power_limit_mw =3D 600*1000; > > } else if (slot_power_limit_mw >=3D 575*1000) { > > value =3D 0xFD; > > slot_power_limit_mw =3D 575*1000; > > } ... > = > This is already implemented in branch: > = > } else if (slot_power_limit_mw <=3D 600*1000) { > value =3D 0xF0 + (slot_power_limit_mw / 1000 - 250) / 25; > scale =3D 0; OK, I was thinking there was a hole here, but I guess not. I think do think it's easier to read and verify if it's structured as "the slot can supply at least X, so advertise X", as opposed to "the slot can supply X or less, so advertise Y". Bjorn _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel