[PATCH v1 2/4] PCI: brcmstb: Add mechanism to turn on subdev regulators
Bjorn Helgaas
helgaas at kernel.org
Wed Jul 6 16:12:50 PDT 2022
On Fri, Jul 01, 2022 at 12:27:23PM -0400, Jim Quinlan wrote:
> Add a mechanism to identify standard PCIe regulators in the DT, allocate
> them, and turn them on before the rest of the bus is scanned during
> pci_host_probe().
>
> The allocated structure that contains the regulators is stored in the port
> driver dev.driver_data field. Here is a point-by-point of how and when
> this mechanism is activated:
>
> If:
> -- PCIe RC driver sets pci_ops {add,remove)_bus to
> pci_subdev_regulators_{add,remove}_bus during its probe.
> -- There is a DT node "RB" under the host bridge DT node.
"RB" isn't mentioned in pcie-brcmstb.c. What's the connection to it?
Is it just an example, and the actual name doesn't matter?
> -- During the RC driver's pci_host_probe() the add_bus callback
> is invoked where (bus->parent && pci_is_root_bus(bus->parent)
> is true
>
> Then:
> -- A struct subdev_regulators structure will be allocated and
> assigned to bus->dev.driver_data.
> -- regulator_bulk_{get,enable} will be invoked on &bus->dev
> and the former will search for and process any
> vpcie{12v,3v3,3v3aux}-supply properties that reside in node "RB".
> -- The regulators will be turned off/on for any unbind/bind operations.
> -- The regulators will be turned off/on for any suspend/resumes, but
> only if the RC driver handles this on its own. This will appear
> in a later commit for the pcie-brcmstb.c driver.
I guess this is all functionality that depends on new properties in
the DT? Prior to this patch, pcie-brcmstb.c didn't do anything at all
with regulators, although brcm,stb-pcie.yaml does mention
"vpcie3v3-supply" in an example.
> The unabridged reason for doing this is as follows. We would like the
> Broadcom STB PCIe root complex driver (and others) to be able to turn
> off/on regulators[1] that provide power to endpoint[2] devices. Typically,
> the drivers of these endpoint devices are stock Linux drivers that are not
> aware that these regulator(s) exist and must be turned on for the driver to
> be probed. The simple solution of course is to turn these regulators on at
> boot and keep them on. However, this solution does not satisfy at least
> three of our usage modes:
>
> 1. For example, one customer uses multiple PCIe controllers, but wants
> the ability to, by script invoking and unbind, turn any or all of them
> and their subdevices off to save power, e.g. when in battery mode.
>
> 2. Another example is when a watchdog script discovers that an endpoint
> device is in an unresponsive state and would like to unbind, power
> toggle, and re-bind just the PCIe endpoint and controller.
>
> 3. Of course we also want power turned off during suspend mode. However,
> some endpoint devices may be able to "wake" during suspend and we need
> to recognise this case and veto the nominal act of turning off its
> regulator. Such is the case with Wake-on-LAN and Wake-on-WLAN support
> where the PCIe endpoint device needs to be kept powered on in order to
> receive network packets and wake the system.
>
> In all of these cases it is advantageous for the PCIe controller to govern
> the turning off/on the regulators needed by the endpoint device. The first
> two cases can be done by simply unbinding and binding the PCIe controller,
> if the controller has control of these regulators.
>
> [1] These regulators typically govern the actual power supply to the
> endpoint chip. Sometimes they may be the official PCIe socket
> power -- such as 3.3v or aux-3.3v. Sometimes they are truly
> the regulator(s) that supply power to the EP chip.
>
> [2] The 99% configuration of our boards is a single endpoint device
> attached to the PCIe controller. I use the term endpoint but it could
> possibly mean a switch as well.
>
> Link: https://lore.kernel.org/r/20220106160332.2143-6-jim2101024@gmail.com
> Signed-off-by: Jim Quinlan <jim2101024 at gmail.com>
> ---
> drivers/pci/controller/pcie-brcmstb.c | 77 +++++++++++++++++++++++++++
> 1 file changed, 77 insertions(+)
>
> diff --git a/drivers/pci/controller/pcie-brcmstb.c b/drivers/pci/controller/pcie-brcmstb.c
> index 2bf5cc399fd0..661d3834c6da 100644
> --- a/drivers/pci/controller/pcie-brcmstb.c
> +++ b/drivers/pci/controller/pcie-brcmstb.c
> @@ -24,6 +24,7 @@
> #include <linux/pci.h>
> #include <linux/pci-ecam.h>
> #include <linux/printk.h>
> +#include <linux/regulator/consumer.h>
> #include <linux/reset.h>
> #include <linux/sizes.h>
> #include <linux/slab.h>
> @@ -283,6 +284,14 @@ static const struct pcie_cfg_data bcm2711_cfg = {
> .bridge_sw_init_set = brcm_pcie_bridge_sw_init_set_generic,
> };
>
> +struct subdev_regulators {
> + unsigned int num_supplies;
> + struct regulator_bulk_data supplies[];
> +};
> +
> +static int pci_subdev_regulators_add_bus(struct pci_bus *bus);
> +static void pci_subdev_regulators_remove_bus(struct pci_bus *bus);
I think these forward declarations are unnecessary. I can remove them
if you agree.
> struct brcm_msi {
> struct device *dev;
> void __iomem *base;
> @@ -436,6 +445,72 @@ static int brcm_pcie_set_ssc(struct brcm_pcie *pcie)
> return ssc && pll ? 0 : -EIO;
> }
>
> +static void *alloc_subdev_regulators(struct device *dev)
> +{
> + static const char * const supplies[] = {
> + "vpcie3v3",
> + "vpcie3v3aux",
> + "vpcie12v",
> + };
> + const size_t size = sizeof(struct subdev_regulators)
> + + sizeof(struct regulator_bulk_data) * ARRAY_SIZE(supplies);
> + struct subdev_regulators *sr;
> + int i;
> +
> + sr = devm_kzalloc(dev, size, GFP_KERNEL);
> + if (sr) {
> + sr->num_supplies = ARRAY_SIZE(supplies);
> + for (i = 0; i < ARRAY_SIZE(supplies); i++)
> + sr->supplies[i].supply = supplies[i];
> + }
> +
> + return sr;
> +}
> +
> +static int pci_subdev_regulators_add_bus(struct pci_bus *bus)
> +{
> + struct device *dev = &bus->dev;
> + struct subdev_regulators *sr;
> + int ret;
> +
> + if (!dev->of_node || !bus->parent || !pci_is_root_bus(bus->parent))
> + return 0;
> +
> + if (dev->driver_data)
> + dev_err(dev, "dev.driver_data unexpectedly non-NULL\n");
I guess you're using the pci_bus dev->driver_data. I don't know of
other users of it, but there's really no ownership model for it. If
it's non-NULL here, it means somebody else, e.g., the PCI core, is
already using it, and when you overwrite it below, you will break that
other user.
I think you should complain and return instead of breaking the other
user. That will mean the regulator won't get enabled and your
endpoint won't work, but I think that's a better way to fail than by
overwriting somebody else's pointer, which may lead to memory
corruption that's very hard to debug.
> + sr = alloc_subdev_regulators(dev);
> + if (!sr)
> + return -ENOMEM;
> +
> + dev->driver_data = sr;
> + ret = regulator_bulk_get(dev, sr->num_supplies, sr->supplies);
> + if (ret)
> + return ret;
> +
> + ret = regulator_bulk_enable(sr->num_supplies, sr->supplies);
> + if (ret) {
> + dev_err(dev, "failed to enable regulators for downstream device\n");
> + return ret;
> + }
> +
> + return 0;
> +}
> +
> +static void pci_subdev_regulators_remove_bus(struct pci_bus *bus)
> +{
> + struct device *dev = &bus->dev;
> + struct subdev_regulators *sr = dev->driver_data;
> +
> + if (!sr || !bus->parent || !pci_is_root_bus(bus->parent))
> + return;
> +
> + if (regulator_bulk_disable(sr->num_supplies, sr->supplies))
> + dev_err(dev, "failed to disable regulators for downstream device\n");
> + regulator_bulk_free(sr->num_supplies, sr->supplies);
> + dev->driver_data = NULL;
> +}
> +
> /* Limits operation to a specific generation (1, 2, or 3) */
> static void brcm_pcie_set_gen(struct brcm_pcie *pcie, int gen)
> {
> @@ -779,6 +854,8 @@ static struct pci_ops brcm_pcie_ops = {
> .map_bus = brcm_pcie_map_conf,
> .read = pci_generic_config_read,
> .write = pci_generic_config_write,
> + .add_bus = pci_subdev_regulators_add_bus,
> + .remove_bus = pci_subdev_regulators_remove_bus,
> };
>
> static struct pci_ops brcm_pcie_ops32 = {
> --
> 2.17.1
>
>
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