linux-kernel - Re: [PATCH v5 17/17] serial: 8250: Add 8250

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Date: Thu, 2 May 2024 16:50:57 +0530
From: Sunil V L <sunilvl@...tanamicro.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-riscv@...ts.infradead.org, linux-acpi@...r.kernel.org,
	linux-pci@...r.kernel.org, linux-serial@...r.kernel.org,
	acpica-devel@...ts.linux.dev,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	"Rafael J . Wysocki" <rafael@...nel.org>,
	Len Brown <lenb@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Anup Patel <anup@...infault.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Samuel Holland <samuel.holland@...ive.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jirislaby@...nel.org>,
	Robert Moore <robert.moore@...el.com>,
	Conor Dooley <conor.dooley@...rochip.com>,
	Andrew Jones <ajones@...tanamicro.com>,
	Marc Zyngier <maz@...nel.org>,
	Atish Kumar Patra <atishp@...osinc.com>,
	Andrei Warkentin <andrei.warkentin@...el.com>,
	Haibo1 Xu <haibo1.xu@...el.com>,
	Björn Töpel <bjorn@...nel.org>
Subject: Re: [PATCH v5 17/17] serial: 8250: Add 8250_acpi driver

On Thu, May 02, 2024 at 01:09:57PM +0300, Andy Shevchenko wrote:
> On Thu, May 02, 2024 at 03:20:08PM +0530, Sunil V L wrote:
> > On Thu, May 02, 2024 at 12:17:59PM +0300, Andy Shevchenko wrote:
> > > On Wed, May 01, 2024 at 05:47:42PM +0530, Sunil V L wrote:
> 
> ...
> 
> > > > + * This driver is for generic 16550 compatible UART enumerated via ACPI
> > > > + * platform bus instead of PNP bus like PNP0501. This is not a full
> > > 
> > > This has to be told in the commit message. Anyway, we don't need a duplication
> > > code, please use 8250_pnp.
> > 
> > Thank you for the review!. Major issue with PNP0501 is, it gets enumerated
> > in a different way which causes issue to get _DEP to work.
> > pnpacpi_init() creates PNP data structures which gets skipped if the
> > UART puts _DEP on the GSI provider (interrupt controller). In that case,
> > we need to somehow reinitialize such PNP devices after interrupt
> > controller gets probed.
> 
> Then fix that code, we don't want a hack driver on top of the existing one for
> the same.
> 
> What I might think out of head is that used IRQ core for your case should
> return a deferred probe error code when it's not ready, then 8250_pnp will
> get reprobed.
> 
Deferred probe was ruled out in prior discussion. Also, deferred probe
will not work with _DEP approach. The reason is, PNP devices itself are
not getting created from the ACPI name space when they have _DEP. Hence,
serial_pnp_probe() will not be called at all.

> > I tried a solution [1] but it required several
> > functions to be moved out of __init. 
> 
> > This driver is not a duplicate of 8250_pnp. It just relies on UART
> > enumerated as platform device instead of using PNP interfaces.
> > Isn't it better and simple to have an option to enumerate as platform
> > device instead of PNP? 
> 
> Ah, then extract platform driver first from 8250_core.c.
> 
Let me know if I understand your suggestion correctly. Do you mean call
something like serial8250_acpi_init() from serial8250_init() and
register the driver directly in serial8250_acpi_init()?

Thanks,
Sunil