linux-kernel - RE: [PATCH v7 1/1] PRUSS UIO driver support

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Date:	Wed, 2 Mar 2011 14:17:42 +0530
From:	"TK, Pratheesh Gangadhar" <pratheesh@...com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"hjk@...sjkoch.de" <hjk@...sjkoch.de>,
	"gregkh@...e.de" <gregkh@...e.de>,
	"sshtylyov@...sta.com" <sshtylyov@...sta.com>,
	"arnd@...db.de" <arnd@...db.de>,
	"Chatterjee, Amit" <amit.chatterjee@...com>,
	"davinci-linux-open-source@...ux.davincidsp.com" 
	<davinci-linux-open-source@...ux.davincidsp.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: RE: [PATCH v7 1/1] PRUSS UIO driver support

Hi,

> From: Thomas Gleixner [mailto:tglx@...utronix.de]
> Sent: Wednesday, March 02, 2011 3:15 AM
> > +
> > +static DEFINE_SPINLOCK(lock);
> > +static struct clk *pruss_clk;
> > +static struct uio_info *info;
> > +static dma_addr_t sram_paddr, ddr_paddr;
> > +static void *prussio_vaddr, *sram_vaddr, *ddr_vaddr;
> > +
> > +static irqreturn_t pruss_handler(int irq, struct uio_info *info)
> > +{
> > +	int intr_bit = (irq - IRQ_DA8XX_EVTOUT0 + 2);
> > +	int val, intr_mask = (1 << intr_bit);
> > +	void __iomem *base = info->mem[0].internal_addr;
> > +	void __iomem *intren_reg = base + PINTC_HIER;
> > +	void __iomem *intrstat_reg = base + PINTC_HIPIR + (intr_bit << 2);
> > +
> > +	spin_lock_irq(&lock);
> 
> No, I said: spin_lock() is sufficient.
Ok. 
> > +	val = ioread32(intren_reg);
> > +	/* Is interrupt enabled and active ? */
> > +	if (!(val & intr_mask) && (ioread32(intrstat_reg) & HIPIR_NOPEND)) {
> > +		spin_unlock_irq(&lock);
> 
> You unconditinally enable interrupts here where you are not supposed
> to do so.
> 
Ok.
> > +		return IRQ_NONE;
> > +	}
> > +
> > +	/* Disable interrupt */
> > +	iowrite32((val & ~intr_mask), intren_reg);

I checked more on this and actually INTC h/w has Host Interrupt
Enable Indexed Set Register (HIEISR) and Host Interrupt Enable Indexed
Clear Register(HIEICR) which I can use to enable/disable interrupts
without doing RMW. I will use these registers and then we don't need
all the spinlock and irqcontrol stuff. So I need to do

iowrite32((intr_bit, HIEICR);// This disable the interrupt bit
in intern_reg.

Userspace can use HIEISR to re-enable the interrupt.

> > +	spin_unlock_irq(&lock);
> > +	return IRQ_HANDLED;
> > +}
> > +
> > +static int pruss_irqcontrol(struct uio_info *info, s32 irq_on)
> > +{
> > +	int intr_bit = info->irq - IRQ_DA8XX_EVTOUT0 + 2;
> > +	int val, intr_mask = (1 << intr_bit);
> > +	void __iomem *base = info->mem[0].internal_addr;
> > +	void __iomem *intren_reg = base + PINTC_HIER;
> > +
> > +	spin_lock_irq(&lock);
> 
> This one is correct, as this is always called from non interrupt
> disabled context.
> 
> > +	val = ioread32(intren_reg);
> > +	if (irq_on)
> > +		iowrite32((val | intr_mask), intren_reg);
> > +	else
> > +		iowrite32((val & ~intr_mask), intren_reg);
> > +	spin_unlock_irq(&lock);
> > +
> > +	return 0;
> > +}
> 
> 
> > +
> > +	spin_lock_init(&lock);
> 
> Sigh. DEFINE_SPINLOCK(lock); already initializes the lock.
> 
> It's not the purpose of a review to tell you what you need to change
> mechanically. Reviewers hint to a correct solution and you are
> supposed to lookup what that solution means and act accordingly. If
> you do not understand the hint or its implications please ask _before_
> sending a new patch set.

Seriously, I went to "fix the comments" mode. Sorry about that. Anyway
I learnt more about things by making mistakes i.e. the positive side.
Thanks a lot for helping us improve on this. 

Pratheesh
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