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Message-ID: <e2842ba1ea0f5dfa818e4cbb9aefe343f48c1e53.camel@ew.tq-group.com>
Date: Wed, 16 Oct 2024 15:14:53 +0200
From: Matthias Schiffer <matthias.schiffer@...tq-group.com>
To: Lee Jones <lee@...nel.org>
Cc: linux@...tq-group.com, linux-kernel@...r.kernel.org, Gregor Herburger
<gregor.herburger@...group.com>
Subject: Re: [PATCH v4 5/5] mfd: tqmx86: add I2C IRQ support
On Wed, 2024-10-16 at 14:07 +0100, Lee Jones wrote:
>
> On Wed, 16 Oct 2024, Matthias Schiffer wrote:
>
> > On Tue, 2024-10-15 at 12:38 +0100, Lee Jones wrote:
> > >
> > > On Mon, 07 Oct 2024, Matthias Schiffer wrote:
> > >
> > > > From: Gregor Herburger <gregor.herburger@...group.com>
> > > >
> > > > The i2c-ocores controller can run in interrupt mode on tqmx86 modules.
> > > > Add module parameter to allow configuring the IRQ number, similar to the
> > > > handling of the GPIO IRQ.
> > > >
> > > > Signed-off-by: Gregor Herburger <gregor.herburger@...group.com>
> > > > Signed-off-by: Matthias Schiffer <matthias.schiffer@...tq-group.com>
> > > > ---
> > > >
> > > > v2: improve module parameter description (was patch 4/4)
> > > > v3: replace IRQ 0 resource with an empty placeholder to simplify error handling
> > > > v4: no changes
> > > >
> > > > drivers/mfd/tqmx86.c | 20 +++++++++++++++++++-
> > > > 1 file changed, 19 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/mfd/tqmx86.c b/drivers/mfd/tqmx86.c
> > > > index e444fcd2a3e9d..057d035b71d33 100644
> > > > --- a/drivers/mfd/tqmx86.c
> > > > +++ b/drivers/mfd/tqmx86.c
> > > > @@ -50,6 +50,7 @@
> > > > #define TQMX86_REG_IO_EXT_INT_9 2
> > > > #define TQMX86_REG_IO_EXT_INT_12 3
> > > > #define TQMX86_REG_IO_EXT_INT_MASK 0x3
> > > > +#define TQMX86_REG_IO_EXT_INT_I2C_SHIFT 0
> > > > #define TQMX86_REG_IO_EXT_INT_GPIO_SHIFT 4
> > > > #define TQMX86_REG_SAUC 0x17
> > > >
> > > > @@ -60,7 +61,16 @@ static uint gpio_irq;
> > > > module_param(gpio_irq, uint, 0);
> > > > MODULE_PARM_DESC(gpio_irq, "GPIO IRQ number (valid parameters: 7, 9, 12)");
> > > >
> > > > -static const struct resource tqmx_i2c_soft_resources[] = {
> > > > +static uint i2c_irq;
> > > > +module_param(i2c_irq, uint, 0);
> > > > +MODULE_PARM_DESC(i2c_irq, "I2C IRQ number (valid parameters: 7, 9, 12)");
> > > > +
> > > > +static struct resource tqmx_i2c_soft_resources[] = {
> > > > + /*
> > > > + * Placeholder for IRQ resource - must come first to be filled in by the
> > > > + * probe function.
> > > > + */
> > > > + {},
> > >
> > > Having a NULLed entry in the first slot doesn't sit well with me at all.
> > >
> > > In order for us to avoid wasting memory, it would be better to place the
> > > entry at the end of the array with a blank entry:
> > >
> > > DEFINE_RES_IRQ(0),
> > >
> > > Later comes the matching code which updates the 0 value to something sane.
> > >
> > > Before you call to the add the devices, check to see if the value has
> > > changed. If it hasn't, deprecate num_resources, effectively masking the
> > > last entry in the array. Then when platform_device_add_resources()
> > > comes to duplicate the array, it will only copy the relevant entries.
> >
> > I chose my current solution because it resulted in more simple and maintainable code:
> >
> > - No dynamic array access, the IRQ resource is always written to index 0
>
> Which is fragile (even with the comment). If you're going to directly
> index array elements, please do so with a unique identifier rather than
> relying on it happening to reside in the first.
>
> > - No surprises regarding num_resources, it is always equal to ARRAY_SIZE(resources)
>
> No surprises, but sometimes it's incorrect.
>
> > It also allowed to make all mfd_cell const; to make num_resources modifyable, either the const would
> > need to be removed, or each mfd_cell would need to be copied to a stack variable in the probe
> > function.
> >
> > In my opinion, these benefits outweigh the 2*64 bytes saved for the additional resources allocated
> > by platform_device_add_resources() - and 128 bytes doesn't seem significant at all, in particular
> > considering that this driver is used on x86_64 only.
>
> But doesn't outweigh my disliking for placing a NULL element at the
> start of the array. If you _must_ do something like this, please place
> it at the end of the array.
>
Ok, will move the placeholder to the end, and access it using a defined index instead of 0. I would
still prefer to keep num_resources constant instead of adjusting it. Does this sound acceptable to
you?
Best,
Matthias
> > >
> > > > DEFINE_RES_IO(TQMX86_IOBASE_I2C, TQMX86_IOSIZE_I2C),
> > > > };
> > > >
> > > > @@ -263,6 +273,14 @@ static int tqmx86_probe(struct platform_device *pdev)
> > > > ocores_platform_data.clock_khz = tqmx86_board_id_to_clk_rate(dev, board_id);
> > > >
> > > > if (i2c_det == TQMX86_REG_I2C_DETECT_SOFT) {
> > > > + if (i2c_irq) {
> > > > + err = tqmx86_setup_irq(dev, "I2C", i2c_irq, io_base,
> > > > + TQMX86_REG_IO_EXT_INT_I2C_SHIFT);
> > > > + if (!err)
> > > > + /* Assumes the IRQ resource placeholder is first */
> > > > + tqmx_i2c_soft_resources[0] = DEFINE_RES_IRQ(i2c_irq);
> > > > + }
> > > > +
> > > > err = devm_mfd_add_devices(dev, PLATFORM_DEVID_NONE,
> > > > tqmx86_i2c_soft_dev,
> > > > ARRAY_SIZE(tqmx86_i2c_soft_dev),
> > > > --
> > > > TQ-Systems GmbH | Mühlstraße 2, Gut Delling | 82229 Seefeld, Germany
> > > > Amtsgericht München, HRB 105018
> > > > Geschäftsführer: Detlef Schneider, Rüdiger Stahl, Stefan Schneider
> > > > https://www.tq-group.com/
> > > >
> > >
> >
> > --
> > TQ-Systems GmbH | Mühlstraße 2, Gut Delling | 82229 Seefeld, Germany
> > Amtsgericht München, HRB 105018
> > Geschäftsführer: Detlef Schneider, Rüdiger Stahl, Stefan Schneider
> > https://www.tq-group.com/
>
--
TQ-Systems GmbH | Mühlstraße 2, Gut Delling | 82229 Seefeld, Germany
Amtsgericht München, HRB 105018
Geschäftsführer: Detlef Schneider, Rüdiger Stahl, Stefan Schneider
https://www.tq-group.com/
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