RE: [PATCH v3] ARM: OMAP: i2c: fix interrupt flood during resume

Shubro,
As Grygorii pointed out we had a generic issue of arm getting interrupted for i2c accesses outside it (IPU in case of omap4/omap5) and to avoid that we would enable/disable mpu level interrupts only when required from i2c-omap driver.

Regards
Huzefa

-----Original Message-----
From: Datta, Shubhrajyoti 
Sent: Friday, October 12, 2012 6:33 AM
To: Strashko, Grygorii
Cc: Kevin Hilman; Kalle Jokiniemi; linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org; w.sang-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org; ben-linux-elnMNo+KYs3YtjvyW6yDsg@public.gmane.org; tony-4v6yS6AI5VpBDgjK7y7TUQ@public.gmane.org; linux-omap-u79uwXL29TY76Z2rM5mHXA@public.gmane.org; Kankroliwala, Huzefa
Subject: Re: [PATCH v3] ARM: OMAP: i2c: fix interrupt flood during resume

On Friday 12 October 2012 03:48 PM, Strashko, Grygorii wrote:

Hi All,

Sorry, for the late reply.
+ CC Huzefa Kankroliwala - who is I2C driver owner on Android Kernel 3.4.

Regarding this patch

hmm I had similar ideas however my idea was to pacify the arm interrupts
when the ip is used by another processor.(something my hw spin patch missed)

Any-ways will wait for Huzefa to comment.

 -  from my point of view, it fixes corner case and not an issue in general.
Let take a look on resume sequence:
   - platform resume
   - syscore resume
   - resume_noirq
   - enable IRQs - resume_device_irqs()
     |- at this point IRQ handler will be invoked if IRQ state is IRQS_PENDING.
     |- so, the I2C device IRQ handler may be called at time when I2C adapter IRQ is still disabled and, as result, the I2C device IRQ-handler may fail. (I2C device and I2C adapter may use different physical IRQ lines)
   - resume_late
     |- enable I2C bus IRQ

Possibly, the better way is to enable/disable I2C bus IRQ when needed - in our case in omap_i2c_xfer().
We use such approach in Android kernel 3.4
(http://git.omapzoom.org/?p=kernel/omap.git;a=commitdiff;h=1445a4d3b587c164bd30d108b61760aaaa07365e)

Grygorii
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