[PATCH 11/27] clocksource: sh_cmt: Add support for multiple channels per device

Hi Magnus,

On Monday 17 February 2014 11:07:06 Magnus Damm wrote:

On Mon, Feb 17, 2014 at 10:48 AM, Laurent Pinchart wrote:

quoted

On Monday 17 February 2014 10:41:31 Magnus Damm wrote:

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On Mon, Feb 17, 2014 at 3:18 AM, Laurent Pinchart wrote:

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On Saturday 15 February 2014 13:46:54 Thomas Gleixner wrote:

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On Fri, 14 Feb 2014, Laurent Pinchart wrote:

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CMT hardware devices can support multiple channels, with global
registers and per-channel registers. The sh_cmt driver currently
models the hardware with one Linux device per channel. This model
makes it difficult to handle global registers in a clean way.

Add support for a new model that uses one Linux device per timer
with multiple channels per device. This requires changes to platform
data, add new channel configuration fields.

Support for the legacy model is kept and will be removed after all
platforms switch to the new model.

Signed-off-by: Laurent Pinchart
[off-list ref]
---

 drivers/clocksource/sh_cmt.c | 299 ++++++++++++++++++++++++--------
 include/linux/sh_timer.h     |   9 ++
 2 files changed, 239 insertions(+), 69 deletions(-)

diff --git a/drivers/clocksource/sh_cmt.c

b/drivers/clocksource/sh_cmt.c
index 5280231..8390f0f 100644

--- a/drivers/clocksource/sh_cmt.c
+++ b/drivers/clocksource/sh_cmt.c

[snip]

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@@ -85,11 +94,15 @@ struct sh_cmt_info {

 struct sh_cmt_channel {
    struct sh_cmt_device *cmt;

-   unsigned int index;
-   void __iomem *base;
+   unsigned int index;     /* Index in the documentation */
+   unsigned int hwidx;     /* Real hardware index */
+
+   void __iomem *iostart;
+   void __iomem *ioctrl;

    struct irqaction irqaction;

While you are at it, can you please get rid of that irqaction and use
request_irq() ?

The driver claims it can't use request_irq() because the function is
not available for early platform devices. If the situation has changed
I'd gladly get rid of irqaction.

With the risk of stating the obvious, this depends on how early the
early platform device stuff is being run. The actual location may not
be the same on SH and ARM for instance.

On ARM we are doing all we can to initialize these devices as late as
ever possible in the MULTIPLAFORM (DT reference) case. Once we manage
to remove the legacy ARM case then there is one less user of early
platform timers.

One perhaps reasonable way forward could be to use request_irq() in
case of DT and leave the legacy platform data case to rely on
irqaction.

The whole point of switching from setup_irq() to request_irq() is to
simplify the code. Adding request_irq() as an option would go in the
opposite direction.

The point of switching to setup_irq() was not very clear to me. I
think it is fine to switch to using it over time, and I'm open to any
alternative ways forward. Usually moving in incremental steps means
more crap in the short term, but if someone could come up with a way
that involves little crap then I'm all for that! =)

I've had a quick look at request_irq(). The function is defined as a static 
inline in include/linux/interrupt.h:

static inline int __must_check
request_irq(unsigned int irq, irq_handler_t handler, unsigned long flags,
            const char *name, void *dev)
{
        return request_threaded_irq(irq, handler, NULL, flags, name, dev);
}

request_threaded_irq() is implemented in kernel/irq/manage.c. I've removed the 
code paths that would never be taken when called by the sh_cmt driver, due to

- handler not being NULL
- thread_fn being NULL
- CONFIG_DEBUG_SHIRQ_FIXME not being set
- IRQF_SHARED not being set

int request_threaded_irq(unsigned int irq, irq_handler_t handler,
                         irq_handler_t thread_fn, unsigned long irqflags,
                         const char *devname, void *dev_id)
{
        struct irqaction *action;
        struct irq_desc *desc;
        int retval;

        desc = irq_to_desc(irq);
        if (!desc)
                return -EINVAL;

        if (!irq_settings_can_request(desc) ||
            WARN_ON(irq_settings_is_per_cpu_devid(desc)))
                return -EINVAL;

        action = kzalloc(sizeof(struct irqaction), GFP_KERNEL);
        if (!action)
                return -ENOMEM;

        action->handler = handler;
        action->thread_fn = thread_fn;
        action->flags = irqflags;
        action->name = devname;
        action->dev_id = dev_id;

        chip_bus_lock(desc);
        retval = __setup_irq(irq, desc, action);
        chip_bus_sync_unlock(desc);

        if (retval)
                kfree(action);

        return retval;
}

setup_irq() is implemented in the same file as

int setup_irq(unsigned int irq, struct irqaction *act)
{
        int retval;
        struct irq_desc *desc = irq_to_desc(irq);

        if (WARN_ON(irq_settings_is_per_cpu_devid(desc)))
                return -EINVAL;
        chip_bus_lock(desc);
        retval = __setup_irq(irq, desc, act);
        chip_bus_sync_unlock(desc);

        return retval;
}

The only two differences between request_irq() and setup_irq() would thus be

- the extra !irq_settings_can_request(desc) check
- the extra kzalloc() call

The former should only be true for chained IRQ handlers, which isn't the case 
here. The latter is just a kmalloc + kmap_atomic + memset as far as I can 
tell.

It thus seems safe to replace setup_irq() with request_irq().

-- 
Regards,

Laurent Pinchart