Re: [PATCH] OMAP: DSS2: Have separate irq handlers for DISPC and DSI

[archit taneja <archit@ti.com>]

Hi,

On Friday 18 February 2011 02:40 PM, Valkeinen, Tomi wrote:
> Hi,
>
> On Thu, 2011-02-17 at 08:25 -0600, Taneja, Archit wrote:
>> Currently, the core DSS platform device requests for an irq line for OMAP2 and
>> OMAP3. Make DISPC and DSI platform devices request for a shared IRQ line.
>>
>> On OMAP3, the logical OR of DSI and DISPC interrupt lines goes to the MPU. There
>> is a register DSS_IRQSTATUS which tells if the interrupt came from DISPC or DSI.
>>
>> On OMAP2, there is no DSI, only DISPC interrupts goto the MPU. There is no
>> DSS_IRQSTATUS register.
>>
>> Hence, it makes more sense to have separate irq handlers corresponding to the
>> DSS sub modules instead of having a common handler.
>>
>> Since on OMAP3 the logical OR of the lines goes to MPU, the irq line is shared
>> among the IRQ handlers.
>>
>> The hwmod irq info has been removed for DSS to DISPC and DSI for OMAP2 and OMAP3
>> hwmod databases. The Probes of DISPC and DSI now request for irq handlers. A dss
>> feature is also added to tell whether the irq lines is shared between DISPC and
>> DSI or not.
>
> Yes, I think this looks much cleaner.
>
> However, I'm not sure if it's necessary to check the DSS_IRQSTATUS. It
> depends a bit on how DSS_IRQSTATUS works. If it just mirrors the
> DISPC/DSI_IRQSTATUS (ie, if there's any bit up in DSI_IRQSTATUS, the DSI
> bit in DSS_IRQSTATUS is up), we can do without it.
>
> For example let's say we haven't enabled any interrupts in DSI, so
> preferably we want to spend as little time in the dsi irq handler as
> possible.
>
> Now, if DSI_IRQSTATUS is all zeroes, and thus DSS_IRQSTATUS.DSI is also
> zero, we can skip the DSI handler by checking DSS_IRQSTATUS.DSI as you
> do in this patch. But we could as well check DSI_IRQSTATUS, and exit if
> it's all zeroes.
>
> If, on the other hand, DSI_IRQSTATUS has any bit up, then also
> DSS_IRQSTATUS.DSI is up, and we have to check the DSI interrupts anyway.
>
> So in both cases the end result is the same, and we can do with less
> code by not using DSS_IRQSTATUS.
>
> However, I'm not 100% sure DSS_IRQSTATUS works like that, but it would
> sound logical and I don't know how could it work otherwise.

I can give it a try.

There is a figure in the OMAP3 TRM titled "DISPC and DSS Interrupts 
tree" which shows its logical OR. How the bits are set in DSS_IRQSTATUS 
is not mentioned anywhere though

>
>   Tomi
>