linux-kernel - Re: [PATCH 1/2] staging: fsl-mc: Allocate IRQ's before scanning DPRC objects

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Message-ID: <5A27FD70.7040208@nxp.com>
Date:   Wed, 6 Dec 2017 14:23:45 +0000
From:   Laurentiu Tudor <laurentiu.tudor@....com>
To:     Bharat Bhushan <bharat.bhushan@....com>,
        Nipun Gupta <nipun.gupta@....com>,
        "stuyoder@...il.com" <stuyoder@...il.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "cakturk@...il.com" <cakturk@...il.com>,
        "bretth256@...il.com" <bretth256@...il.com>,
        "arnd@...db.de" <arnd@...db.de>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>
Subject: Re: [PATCH 1/2] staging: fsl-mc: Allocate IRQ's before scanning DPRC
 objects

Hi Bharat,

On 12/06/2017 04:03 PM, Bharat Bhushan wrote:
> Hi Laurentiu,
>
>> -----Original Message-----
>> From: Laurentiu Tudor
>> Sent: Wednesday, December 06, 2017 7:00 PM
>> To: Nipun Gupta <nipun.gupta@....com>; stuyoder@...il.com; Bharat
>> Bhushan <bharat.bhushan@....com>; gregkh@...uxfoundation.org;
>> cakturk@...il.com; bretth256@...il.com; arnd@...db.de
>> Cc: linux-kernel@...r.kernel.org; devel@...verdev.osuosl.org
>> Subject: Re: [PATCH 1/2] staging: fsl-mc: Allocate IRQ's before scanning DPRC
>> objects
>>
>> Hi Nipun,
>>
>> Can you polish a bit this commit message? It doesn't seem to explain why this
>> is needed.
>>
>> On 12/06/2017 06:18 PM, Nipun Gupta wrote:
>>> When DPRC probing is deferred (such as where IOMMU is not probed
>>> before the fsl-mc bus), all the devices in the DPRC containers gets
>>> initialized one after another.
>>
>> Are you referring to dprc probing being deferred (do we ever do that?) or
>> devices inside the dprc deferring the probe?
>>
>>> As IRQ's were allocated only once the
>>> DPRC scanning is completed, the devices like DPIO which uses these
>>> IRQ's at initalization fails. This patch allocates the IRQ resources
>>
>> s/initalization/initialization
>>
>>> before scanning all the objects in the DPRC container.
>>>
>>> Signed-off-by: Nipun Gupta <nipun.gupta@....com>
>>> ---
>>>    drivers/staging/fsl-mc/bus/dprc-driver.c | 49 ++++++++++++++++++------
>> --------
>>>    1 file changed, 27 insertions(+), 22 deletions(-)
>>>
>>> diff --git a/drivers/staging/fsl-mc/bus/dprc-driver.c
>>> b/drivers/staging/fsl-mc/bus/dprc-driver.c
>>> index 06df528..7265431 100644
>>> --- a/drivers/staging/fsl-mc/bus/dprc-driver.c
>>> +++ b/drivers/staging/fsl-mc/bus/dprc-driver.c
>>> @@ -206,7 +206,8 @@ static void dprc_add_new_devices(struct
>> fsl_mc_device *mc_bus_dev,
>>>     * dprc_scan_objects - Discover objects in a DPRC
>>>     *
>>>     * @mc_bus_dev: pointer to the fsl-mc device that represents a DPRC
>>> object
>>> - * @total_irq_count: total number of IRQs needed by objects in the DPRC.
>>> + * @total_irq_count: If argument is provided the function populates
>>> + the
>>> + * total number of IRQs created by objects in the DPRC.
>>
>> As a side node, after a cursory look i noticed that this total_irq_count
>> parameter is used only for some sanity checks. I'm thinking of dropping it in a
>> follow-up cleanup patch.
>
> How you will ensure that number of IRQ needed are not sufficient for devices in the container?
> Do you think we need to either not enable additional devices or add irqs to irq-pool ?

In the current implementation we allocate a pool of 
FSL_MC_IRQ_POOL_MAX_TOTAL_IRQS (= 256) no mater what total_irq_count is.
I think this is enough for our current scenarios, but if in the future 
we ever hit this limit we can think of a mechanism along the lines of 
your example. Adding another chunk of irqs to the pool seems to me like 
a good idea in the future.

---
Best Regards, Laurentiu