01.11.2019 13:18, Thierry Reding пишет:
> On Thu, Oct 31, 2019 at 06:11:33PM +0300, Dmitry Osipenko wrote:
>> 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.
>
> Good catch. I've added that (and the module_put() from below) to the
> patch.
>
>>> + 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.
>
> This has the slight disadvantage that we would have to iterate over a
> number of compatible strings in case we want to transparently support
> more than a single version of the memory controller.
Good point.
> An alternative, which is used by a number of other resource registry
> APIs, would be to work with lookup tables. Basically those would make
> a mapping between a provider and a device/consumer pair. The result
> would look something like this:
>
> struct memory_controller_lookup {
> const char *provider;
> const char *dev_id;
> const char *con_id;
> };
>
> static const struct memory_controller_lookup *tegra124_mc_lookup[] = {
> { "70019000.memory-controller", "6000c800.actmon", NULL },
> };
>
> memory_controller_get() could then use that as a last-resort to find a
> reference to a memory controller if a device tree phandle isn't
> available.
The explicit lookup table sounds like a good idea because it should be
usable in a case of a non-OF devices as well.
> On the other hand it should be fairly easy to conditionalize all the
> code based purely on the availability of a phandle:
>
> mc = memory_controller_get(dev, NULL);
> if (IS_ERR(mc)) {
> if (mc != ERR_PTR(-ENODEV))
> return PTR_ERR(mc);
>
> mc = NULL;
> }
>
> ...
>
> if (mc) {
> ...
> }
>
> The above could be simplified by wrapping the logic in a helper that can
> be used if consumers can work without: memory_controller_get_optional().
Optional retrieval helpers are a common thing among subsystem APIs.
Although it probably shouldn't be necessary for the start of the MC API
and could be added later on, once there will be a real need in it.
AFAIK, none of the Tegra drivers have such a need right now.
