linux-kernel - Re: [Patch V6 2/6] irqchip: xilinx: Clean up irqdomain argument and read/write

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Date:   Tue, 1 Nov 2016 11:05:43 +0000
From:   Zubair Lutfullah Kakakhel <Zubair.Kakakhel@...tec.com>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     <monstr@...str.eu>, <jason@...edaemon.net>, <marc.zyngier@....com>,
        <linux-kernel@...r.kernel.org>, <michal.simek@...inx.com>,
        <linuxppc-dev@...ts.ozlabs.org>, <mpe@...erman.id.au>
Subject: Re: [Patch V6 2/6] irqchip: xilinx: Clean up irqdomain argument and
 read/write

Hi,

Thanks for the review.

On 10/31/2016 07:51 PM, Thomas Gleixner wrote:
> On Mon, 31 Oct 2016, Zubair Lutfullah Kakakhel wrote:
>> The drivers read/write function handling is a bit quirky.
>
> Can you please explain in more detail what's quirky and why it should be
> done differently,
>
>> And the irqmask is passed directly to the handler.
>
> I can't make any sense out of that sentence.  Which handler? If you talk
> about the write function, then I don't see a change. So what are you
> talking about?

Thanks. I'll add more detail in v7 if this patch survives.

>
>> Add a new irqchip struct to pass to the handler and
>> cleanup read/write handling.
>
> I still don't see what it cleans up. You move the write function pointer
> into a data structure, which is exposed by another pointer. So you create
> two levels of indirection in the hotpath. The function prototype is still
> the same. So all this does is making things slower unless I'm missing
> something.

I wrote this patch/cleanup based on a review of driver by Marc when I moved the
driver from arch/microblaze to drivers/irqchip

"Marc Zyngier

...

 >  arch/microblaze/kernel/intc.c   | 196 ----------------------------------------
 >  drivers/irqchip/irq-axi-intc.c  | 196 ++++++++++++++++++++++++++++++++++++++++

...

 > +	/* Yeah, okay, casting the intr_mask to a void* is butt-ugly, but I'm
 > +	 * lazy and Michal can clean it up to something nicer when he tests
 > +	 * and commits this patch.  ~~gcl */
 > +	root_domain = irq_domain_add_linear(intc, nr_irq, &xintc_irq_domain_ops,
 > +							(void *)intr_mask);

Since you're now reworking this driver, how about addressing this
ugliness? You could store the intr_mask together with intc_baseaddr,
and the read/write functions in a global structure, and pass a
pointer to it? That would make the code a bit nicer...
"

https://patchwork.kernel.org/patch/9287933/

>
>> -static unsigned int (*read_fn)(void __iomem *);
>> -static void (*write_fn)(u32, void __iomem *);
>> +struct xintc_irq_chip {
>> +	void __iomem *base;
>> +	struct	irq_domain *domain;
>> +	struct	irq_chip chip;
>
> The tabs between struct and the structure name are bogus.
>
>> +	u32	intr_mask;
>> +	unsigned int (*read)(void __iomem *iomem);
>> +	void (*write)(u32 data, void __iomem *iomem);
>
> Please structure that like a table:
>
> 	void			__iomem *base;
> 	struct irq_domain	*domain;
> 	struct irq_chip		chip;
> 	u32			intr_mask;
> 	unsigned int		(*read)(void __iomem *iomem);
> 	void			(*write)(u32 data, void __iomem *iomem);
>
> Can you see how that makes parsing the struct simpler, because the data
> types are clearly to identify?

That does make it look much better.

>
>> +static struct xintc_irq_chip *xintc_irqc;
>>
>>  static void intc_write32(u32 val, void __iomem *addr)
>>  {
>> @@ -54,6 +60,18 @@ static unsigned int intc_read32_be(void __iomem *addr)
>>  	return ioread32be(addr);
>>  }
>>
>> +static inline unsigned int xintc_read(struct xintc_irq_chip *xintc_irqc,
>> +					     int reg)
>> +{
>> +	return xintc_irqc->read(xintc_irqc->base + reg);
>> +}
>> +
>> +static inline void xintc_write(struct xintc_irq_chip *xintc_irqc,
>> +				     int reg, u32 data)
>> +{
>> +	xintc_irqc->write(data, xintc_irqc->base + reg);
>> +}
>> +
>>  static void intc_enable_or_unmask(struct irq_data *d)
>>  {
>>  	unsigned long mask = 1 << d->hwirq;
>> @@ -65,21 +83,21 @@ static void intc_enable_or_unmask(struct irq_data *d)
>>  	 * acks the irq before calling the interrupt handler
>>  	 */
>>  	if (irqd_is_level_type(d))
>> -		write_fn(mask, intc_baseaddr + IAR);
>> +		xintc_write(xintc_irqc, IAR, mask);
>
> So this whole thing makes only sense, when you want to support multiple
> instances of that chip and then you need to store the xintc_irqc pointer as
> irqchip data and retrieve it from there. Unless you do that, this "cleanup"
> is just churn for nothing with the effect of making things less efficient.
>

Indeed the driver doesn't support multiple instances of the Xilinx Interrupt controller.
I don't have a use-case or the hardware for that.

So what would be the recommended course of action?

Regards,
ZubairLK

> Thanks,
>
> 	tglx
>