linuxsh-dev

Irq priorities

[EXTERNAL B. M. (P. ST-FIR/Eng) <ext...@de...>]

Hi there,

I have a question about the priority for the irqs.=20
I found that the priorities for the other CPUs, set in the setup-sh*.c
are set as followed:
low priority (2) for timers
low priority (3) for sci(f)=20
high priority (7) for dma
This doesn't make sens to me. I would give timers a high priority, so
they keep acurate and dma a low priority.=20

Are there any rules for setting the priority for interrupts?=20

Regards

Markus

Re: Irq priorities

[Manuel L. <ma...@ro...>]

Howdy,

On Wed, Jun 27, 2007 at 02:56:39PM +0200, EXTERNAL Brunner Markus (Praktikant;  ST-FIR/Eng) wrote:

> I have a question about the priority for the irqs. 
> I found that the priorities for the other CPUs, set in the setup-sh*.c
> are set as followed:
> low priority (2) for timers
> low priority (3) for sci(f) 
> high priority (7) for dma
> This doesn't make sens to me. I would give timers a high priority, so
> they keep acurate and dma a low priority. 
> 
> Are there any rules for setting the priority for interrupts? 

I guess this depends on the application the system is intended for.
I set DMABRG priority high on the SH7760 because audio needs them to
be handled as soon as possible (especially if you want to do low-latency
mixing and stuff [but that's impossible on the 7760 anyway ;-) ])

So I suggest you set priorities according to your specific needs.

	Manuel Lauss

Re: Irq priorities

[Paul M. <pau...@re...>]

On Wed, Jun 27, 2007 at 02:56:39PM +0200, EXTERNAL Brunner Markus (Praktikant;  ST-FIR/Eng) wrote:
> I have a question about the priority for the irqs. 
> I found that the priorities for the other CPUs, set in the setup-sh*.c
> are set as followed:
> low priority (2) for timers
> low priority (3) for sci(f) 
> high priority (7) for dma
> This doesn't make sens to me. I would give timers a high priority, so
> they keep acurate and dma a low priority. 
> 
> Are there any rules for setting the priority for interrupts? 
> 
Not really. I suppose we should add an abstraction to the hardirq
framework for setting the IRQ priority, as other platforms care too. I
still have some patches for this floating around from way back when, so
I'll dig those up and see what the other architecture folks think.

It's traditionally been kept in the platform setup code so the system
integrator can decide which priority levels to ship with for their
application. Pushing it down to the drivers might help for the cases
where we _know_ we can tolerate a low priority on the IRQ. We just don't
want to run in to the situation where everyone sets their IRQ to the
highest priority and weird things start happening with the more important
peripherals.

RE: Irq priorities

[Carmelo S. <lin...@st...>]

On our 7109 board we exported the symbol set_intc2_irq_priority_mod from the
kernel file arch/sh/kernel/cpu/irq/intc2.c so that the driver can set its
own interrupt priority. However it is better to have only one entry point
for setting all of them so that it would make it easy to tune the system
during the final stage of the integration. 
Lino.
  


-----Original Message-----
From: lin...@li...
[mailto:lin...@li...] On Behalf Of Paul Mundt
Sent: Friday, July 06, 2007 10:48 AM
To: EXTERNAL Brunner Markus (Praktikant; ST-FIR/Eng)
Cc: lin...@li...
Subject: Re: Irq priorities

On Wed, Jun 27, 2007 at 02:56:39PM +0200, EXTERNAL Brunner Markus
(Praktikant;  ST-FIR/Eng) wrote:
> I have a question about the priority for the irqs. 
> I found that the priorities for the other CPUs, set in the setup-sh*.c
> are set as followed:
> low priority (2) for timers
> low priority (3) for sci(f) 
> high priority (7) for dma
> This doesn't make sens to me. I would give timers a high priority, so
> they keep acurate and dma a low priority. 
> 
> Are there any rules for setting the priority for interrupts? 
> 
Not really. I suppose we should add an abstraction to the hardirq
framework for setting the IRQ priority, as other platforms care too. I
still have some patches for this floating around from way back when, so
I'll dig those up and see what the other architecture folks think.

It's traditionally been kept in the platform setup code so the system
integrator can decide which priority levels to ship with for their
application. Pushing it down to the drivers might help for the cases
where we _know_ we can tolerate a low priority on the IRQ. We just don't
want to run in to the situation where everyone sets their IRQ to the
highest priority and weird things start happening with the more important
peripherals.

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