linux-kernel - Re: [PATCH net-next v3 08/19] net: ravb: Move the IRQs get and request in the probe function

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Date: Tue, 9 Jan 2024 23:47:47 +0300
From: Sergey Shtylyov <s.shtylyov@....ru>
To: claudiu beznea <claudiu.beznea@...on.dev>, <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 1/8/24 11:58 AM, 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!
> 
>>> 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...

> 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...

[...]

MBR, Sergey