linux-kernel - Re: [RFC PATCH] Bluetooth: btnxpuart: Fix nxp

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Date: Wed, 17 Jan 2024 12:19:27 +0100
From: Francesco Dolcini <francesco@...cini.it>
To: Neeraj Sanjay Kale <neeraj.sanjaykale@....com>
Cc: Francesco Dolcini <francesco@...cini.it>,
	"marcel@...tmann.org" <marcel@...tmann.org>,
	"johan.hedberg@...il.com" <johan.hedberg@...il.com>,
	"luiz.dentz@...il.com" <luiz.dentz@...il.com>,
	Marcel Ziswiler <marcel.ziswiler@...adex.com>,
	Amitkumar Karwar <amitkumar.karwar@....com>,
	"linux-bluetooth@...r.kernel.org" <linux-bluetooth@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Sherry Sun <sherry.sun@....com>, Rohit Fule <rohit.fule@....com>
Subject: Re: [RFC PATCH] Bluetooth: btnxpuart: Fix nxp_setup in case chip is
 powered on late

On Wed, Jan 17, 2024 at 11:11:44AM +0000, Neeraj Sanjay Kale wrote:
> > > Here, the driver probe registers an hci interface
> > > (hci_register_dev()), and returns success to kernel.
> > >
> > > The hci_register_dev() queues hdev->power_on work at the end, which
> > > opens the hci dev, and ultimately calls this setup function.
> > >
> > > In this patch, we are queueing the same work from the delayed
> > > setup_retry_work().
> > >
> > > Returning -ENODEV (or -EPROBE_DEFER) would only affect hci_dev_open(),
> > > which is in power_on work context, and not driver probe context.
> > >
> > > Perhaps, we should call it hci_retry_power_on() work or something
> > > similar?
> > >
> > > Please let me know your thoughts on this.
> > 
> > Do you see any way to get rid of this complexity? Maybe having this check
> > done during probe, deferring there till we know the device is in a suitable
> > state (e.g. either you received the bootloader signature, you know the device
> > is powered or that the firmware is loaded and ready?).
> > 
> > In other words returning EPROBE_DEFER before calling hci_register_dev()?
> > 
> Unfortunately no. To read any bootloader signatures, or read CTS line,
> we need serdev device opened, which is done only after
> hci_register_dev() -> power_on work -> hci_dev_open()->serdev_open().

Ok, thanks, it makes sense and it's clear.

> We could simplify this by only returning -ENODEV, without the
> delayed_work handling, but then user would have to remove and
> re-insert the btnxpuart driver after mwifiex driver is loaded
> successfully.
>
> This may not seam like a user-friendly approach.

I think that something like that is pretty much useless, manual
reloading is already possible, and this can also be solved
"artificially" serializing loading the wifi driver and the bt one (the
latter is what we are currently doing to overcome this limitation).

Francesco