Subject: Re: [PATCH v2 2/4] irqchip/meson-gpio: support more than 8 channels gpio irq line

From: Marc Zyngier <[email-masked]>
Date: Wed, 19 Jan 2022 13:31:58 +0000

On Wed, 19 Jan 2022 07:08:07 +0000,
Qianggui Song <[email-masked]> wrote:
> 
> Current meson gpio irqchip driver only support 8 channels for gpio irq
> line, later chips may have more then 8 channels, so need to modify code
> to support more.
> 
> Signed-off-by: Qianggui Song <[email-masked]>
> ---
>  drivers/irqchip/irq-meson-gpio.c | 33 +++++++++++++++++++++++---------
>  1 file changed, 24 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/irqchip/irq-meson-gpio.c b/drivers/irqchip/irq-meson-gpio.c
> index d90ff0b92480..eefe15e1b3a6 100644
> --- a/drivers/irqchip/irq-meson-gpio.c
> +++ b/drivers/irqchip/irq-meson-gpio.c
> @@ -16,7 +16,6 @@
>  #include <linux/of.h>
>  #include <linux/of_address.h>
>  
> -#define NUM_CHANNEL 8
>  #define MAX_INPUT_MUX 256
>  
>  #define REG_EDGE_POL	0x00
> @@ -60,6 +59,7 @@ struct irq_ctl_ops {
>  
>  struct meson_gpio_irq_params {
>  	unsigned int nr_hwirq;
> +	unsigned int nr_channels;
>  	bool support_edge_both;
>  	unsigned int edge_both_offset;
>  	unsigned int edge_single_offset;
> @@ -81,6 +81,7 @@ struct meson_gpio_irq_params {
>  	.edge_single_offset = 0,				\
>  	.pol_low_offset = 16,					\
>  	.pin_sel_mask = 0xff,					\
> +	.nr_channels = 8,					\
>  
>  #define INIT_MESON_A1_COMMON_DATA(irqs)				\
>  	INIT_MESON_COMMON(irqs, meson_a1_gpio_irq_init,		\
> @@ -90,6 +91,7 @@ struct meson_gpio_irq_params {
>  	.edge_single_offset = 8,				\
>  	.pol_low_offset = 0,					\
>  	.pin_sel_mask = 0x7f,					\
> +	.nr_channels = 8,					\
>  
>  static const struct meson_gpio_irq_params meson8_params = {
>  	INIT_MESON8_COMMON_DATA(134)
> @@ -136,8 +138,8 @@ static const struct of_device_id meson_irq_gpio_matches[] = {
>  struct meson_gpio_irq_controller {
>  	const struct meson_gpio_irq_params *params;
>  	void __iomem *base;
> -	u32 channel_irqs[NUM_CHANNEL];
> -	DECLARE_BITMAP(channel_map, NUM_CHANNEL);
> +	u32 *channel_irqs;
> +	unsigned long *channel_map;

This really is over-engineering at its best.

With your new fancy HW, you have at most 12 bits being used in this
bitmap. So why not have a single unsigned long, no dynamic allocation,
and simply an assertion somewhere that checks that nr_channel is never
bigger than BITS_PER_LONG? Less code, less memory wasted, less problems.

	M.

-- 
Without deviation from the norm, progress is not possible.

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