15.10.2019 19:29, Thierry Reding пишет:
> From: Thierry Reding <treding@xxxxxxxxxx>
>
> This new framework is currently nothing more than a registry of memory
> controllers, with the goal being to order device probing. One use-case
> where this is useful, for example, is a memory controller device which
> needs to program some registers before the system MMU can be enabled.
> Associating the memory controller with the SMMU allows the SMMU driver
> to defer the probe until the memory controller has been registered.
>
> One such example is Tegra186 where the memory controller contains some
> registers that are used to program stream IDs for the various memory
> clients (display, USB, PCI, ...) in the system. Programming these SIDs
> is required for the memory clients to emit the proper SIDs as part of
> their memory requests. The memory controller driver therefore needs to
> be programmed prior to the SMMU driver. To achieve that, the memory
> controller will be referenced via phandle from the SMMU device tree
> node, the SMMU driver can then use the memory controller framework to
> find it and defer probe until it has been registered.
>
> Signed-off-by: Thierry Reding <treding@xxxxxxxxxx>
> ---
> drivers/memory/Makefile | 1 +
> drivers/memory/core.c | 99 +++++++++++++++++++++++++++++++
> include/linux/memory-controller.h | 25 ++++++++
> 3 files changed, 125 insertions(+)
> create mode 100644 drivers/memory/core.c
> create mode 100644 include/linux/memory-controller.h
Hello Thierry,
This looks like a very good endeavour! I have couple comments, please
see them below.
> diff --git a/drivers/memory/Makefile b/drivers/memory/Makefile
> index 27b493435e61..d16e7dca8ef9 100644
> --- a/drivers/memory/Makefile
> +++ b/drivers/memory/Makefile
> @@ -3,6 +3,7 @@
> # Makefile for memory devices
> #
>
> +obj-y += core.o
> obj-$(CONFIG_DDR) += jedec_ddr_data.o
> ifeq ($(CONFIG_DDR),y)
> obj-$(CONFIG_OF) += of_memory.o
> diff --git a/drivers/memory/core.c b/drivers/memory/core.c
> new file mode 100644
> index 000000000000..1772e839305a
> --- /dev/null
> +++ b/drivers/memory/core.c
> @@ -0,0 +1,99 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2019 NVIDIA Corporation.
> + */
> +
> +#include <linux/memory-controller.h>
> +#include <linux/of.h>
> +
> +static DEFINE_MUTEX(controllers_lock);
> +static LIST_HEAD(controllers);
> +
> +static void memory_controller_release(struct kref *ref)
> +{
> + struct memory_controller *mc = container_of(ref, struct memory_controller, ref);
> +
> + WARN_ON(!list_empty(&mc->list));
> +}
> +
> +int memory_controller_register(struct memory_controller *mc)
> +{
> + kref_init(&mc->ref);
> +
> + mutex_lock(&controllers_lock);
> + list_add_tail(&mc->list, &controllers);
> + mutex_unlock(&controllers_lock);
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(memory_controller_register);
> +
> +void memory_controller_unregister(struct memory_controller *mc)
> +{
> + mutex_lock(&controllers_lock);
> + list_del_init(&mc->list);
> + mutex_unlock(&controllers_lock);
> +
> + kref_put(&mc->ref, memory_controller_release);
> +}
> +EXPORT_SYMBOL_GPL(memory_controller_unregister);
> +
> +static struct memory_controller *
> +of_memory_controller_get(struct device *dev, struct device_node *np,
> + const char *con_id)
> +{
> + const char *cells = "#memory-controller-cells";
> + const char *names = "memory-controller-names";
> + const char *prop = "memory-controllers";
> + struct memory_controller *mc;
> + struct of_phandle_args args;
> + int index = 0, err;
> +
> + if (con_id) {
> + index = of_property_match_string(np, names, con_id);
> + if (index < 0)
> + return ERR_PTR(index);
> + }
> +
> + err = of_parse_phandle_with_args(np, prop, cells, index, &args);
> + if (err) {
> + if (err == -ENOENT)
> + err = -ENODEV;
> +
> + return ERR_PTR(err);
> + }
> +
> + mutex_lock(&controllers_lock);
> +
> + list_for_each_entry(mc, &controllers, list) {
> + if (mc->dev && mc->dev->of_node == args.np) {
> + kref_get(&mc->ref);
This is not enough because memory controller driver could be a loadable
module, thus something like this is needed here:
__module_get(mc->dev->driver->owner);
This won't allow MC driver to be unloaded while it has active users.
> + mutex_unlock(&controllers_lock);
> + goto unlock;
> + }
> + }
> +
> + mc = ERR_PTR(-EPROBE_DEFER);
> +
> +unlock:
> + mutex_unlock(&controllers_lock);
> + of_node_put(args.np);
> + return mc;
> +}
> +
> +struct memory_controller *
> +memory_controller_get(struct device *dev, const char *con_id)
> +{
> + if (IS_ENABLED(CONFIG_OF) && dev && dev->of_node)
> + return of_memory_controller_get(dev, dev->of_node, con_id);
> +
> + return ERR_PTR(-ENODEV);
> +}
> +EXPORT_SYMBOL_GPL(memory_controller_get);
In most cases memory controllers are unique in a system, so it looks to
me that it will be more universal to have ability to get MC by its
device-tree compatible name. Like this:
of_memory_controller_get_by_compatible(const char *compatible);
This will allow current drivers (like Tegra20 devfreq driver for
example) to utilize this new API without having trouble of maintaining
backwards compatibility with older device-trees that do not have a
phandle to MC.
https://elixir.bootlin.com/linux/v5.4-rc5/source/drivers/devfreq/tegra20-devfreq.c#L100
Of course there could be cases where there are multiple controllers with
the same compatible, but that case could be supported later on by those
who really need it. I don't think that any of NVIDIA Tegra SoCs fall
into that category.
> +void memory_controller_put(struct memory_controller *mc)
> +{
> + if (mc)
> + kref_put(&mc->ref, memory_controller_release);
module_put(mc->dev->driver->owner);
> +}
> +EXPORT_SYMBOL_GPL(memory_controller_put);
[snip]
