Date: Mon, 15 Jan 2024 09:10:25 +0200
From: claudiu beznea <claudiu.beznea@...on.dev>
To: Sergey Shtylyov <s.shtylyov@....ru>, davem@...emloft.net,
 edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
 richardcochran@...il.com, p.zabel@...gutronix.de,
 yoshihiro.shimoda.uh@...esas.com, wsa+renesas@...g-engineering.com
Cc: netdev@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
 linux-kernel@...r.kernel.org, geert+renesas@...der.be,
 Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
Subject: Re: [PATCH net-next v3 08/19] net: ravb: Move the IRQs get and
 request in the probe function



On 14.01.2024 20:07, Sergey Shtylyov wrote:
> On 1/10/24 2:55 PM, claudiu beznea wrote:
> 
> [...]
> 
>>>>>> From: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
>>>>>>
>>>>>> The runtime PM implementation will disable clocks at the end of
>>>>>> ravb_probe(). As some IP variants switch to reset mode as a result of
>>>>>> setting module standby through clock disable APIs, to implement runtime PM
>>>>>> the resource parsing and requesting are moved in the probe function and IP
>>>>>> settings are moved in the open function. This is done because at the end of
>>>>>> the probe some IP variants will switch anyway to reset mode and the
>>>>>> registers content is lost. Also keeping only register specific operations
>>>>>> in the ravb_open()/ravb_close() functions will make them faster.
>>>>>>
>>>>>> Commit moves IRQ requests to ravb_probe() to have all the IRQs ready when
>>>>>> the interface is open. As now IRQs gets and requests are in a single place
>>>>>> there is no need to keep intermediary data (like ravb_rx_irqs[] and
>>>>>> ravb_tx_irqs[] arrays or IRQs in struct ravb_private).
>>>>>
>>>>>    There's one thing that you probably didn't take into account: after
>>>>> you call request_irq(), you should be able to handle your IRQ as it's
>>>>> automatically unmasked, unless you pass IRQF_NO_AUTOEN to request_irq().
>>>>> Your device may be held i reset or even powered off but if you pass
>>>>> IRQF_SHARED to request_irq() (you do in a single IRQ config), you must
>>>>> be prepared to get your device's registers read (in order to ascertain
>>>
>>>    And, at least on arm32, reading a powered off (or not clocked?) device's
>>> register causes an imprecise external abort exception -- which results in a
>>> kernel oops...
>>>
>>>>> whether it's your IRQ or not). And you can't even pass IRQF_NO_AUTOEN
>>>>> along with IRQF_SHARED, according to my reading of the IRQ code...
>>>>
>>>> Good point!
> 
>    Iff we can come up with a robust check whether the device is powered on,
> we can overcome even the IRQF_SHARED issue though...
>    I'm seeing pm_runtime_active() API and wondering whether we can use it
> from the IRQ context. Alternatively, we can add a is_opened flag, like
> sh_eth.c does...

The is_open flag should deal with this, too, AFAICT at the moment, and
should also cover your concerns about U-Boot.

Thank you,
Claudiu Beznea

> 
>>>>>> This is a preparatory change to add runtime PM support for all IP variants.
>>>>>
>>>>>   I don't readily see why this is necessary for the full-fledged RPM
>>>>> support...
>>>>
>>>> I tried to speed up the ravb_open()/ravb_close() but missed the IRQF_SHARED
>>>
>>>    I doubt that optimizing ravb_{open,close}() is worth pursuing, frankly...
> 
>    OTOH, we'll get a simpler/cleaner code if we do this...
>    Previously, I was under an impression that it's common behavior of
> the networking drivers to call request_irq() from their ndo_open() methods.
> Apparently, it's not true anymore (probably with the introduction of the
> managed device API) -- the newer drivers often call devm_request_irq()
> from their probe() methods instead...
> 
>>>> IRQ. As there is only one IRQ requested w/ IRQF_SHARED, are you OK with
>>>> still keeping the rest of IRQs handled as proposed by this patch?
>>>
>>>    I'm not, as this doesn't really seem necessary for your main goal.
>>> It's not clear in what state U-Boot leaves EtherAVB...
> 
>    This still seems an issue though... My prior experience with the R-Car
> MMC driver tells me that U-Boot may leave interrupts enabled... :-/
> 
>> Ok. One other reason I did this is, as commit message states, to keep
>> resource parsing and allocation/freeing in probe/remove and hardware
>> settings in open/close.
>>  
>> Anyway, I'll revert all the changes IRQ related.
> 
>    Now I've changed my mind -- let's retain your patch! It needs some work
> though...
> 
>> Thank you,
>> Claudiu Beznea
> 
> [...]
> 
> MBR, Sergey

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