linux-kernel - RE: [PATCH v9 tty-next 2/4] serial: 8250_pci1xxxx: Add driver for quad-uart support

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Message-ID: <PH7PR11MB5958956CB3DFD8E9B4A122379BE69@PH7PR11MB5958.namprd11.prod.outlook.com>
Date:   Fri, 16 Dec 2022 09:30:42 +0000
From:   <Tharunkumar.Pasumarthi@...rochip.com>
To:     <andriy.shevchenko@...ux.intel.com>
CC:     <Kumaravel.Thiagarajan@...rochip.com>,
        <linux-kernel@...r.kernel.org>, <linux-serial@...r.kernel.org>,
        <gregkh@...uxfoundation.org>, <jirislaby@...nel.org>,
        <ilpo.jarvinen@...ux.intel.com>, <macro@...am.me.uk>,
        <cang1@...e.co.uk>, <colin.i.king@...il.com>,
        <phil.edworthy@...esas.com>, <biju.das.jz@...renesas.com>,
        <geert+renesas@...der.be>, <lukas@...ner.de>,
        <u.kleine-koenig@...gutronix.de>, <wander@...hat.com>,
        <etremblay@...tech-controls.com>, <jk@...abs.org>,
        <UNGLinuxDriver@...rochip.com>
Subject: RE: [PATCH v9 tty-next 2/4] serial: 8250_pci1xxxx: Add driver for
 quad-uart support

> From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Sent: Friday, December 16, 2022 1:56 PM
> To: Tharunkumar Pasumarthi - I67821
> <Tharunkumar.Pasumarthi@...rochip.com>
> Subject: Re: [PATCH v9 tty-next 2/4] serial: 8250_pci1xxxx: Add driver for
> quad-uart support
> 
> > > > +             pci_iounmap(pdev, priv->membase);
> > >
> > > Here is inconsistency on how you interpret pci_*() calls when
> > > pcim_enable_device() has been used. I.e. for IRQ you don't
> > > deallocate resources explicitly (yes, it's done automatically
> > > anyway), but you explicitly call pci_iounmap(). Choose a single approach
> for all of them.
> >
> > AFAIK call to pci_iounmap cannot be avoided since pci_ioremap_bar is not
> 'managed' API.
> > You suggest calling pci_free_irq_vectors (even though it is not mandatory)?
> 
> Why is it not mandatory?

Hi Andy,

Following is the reason why I felt calling pci_free_irq_vectors is not mandatory.
Correct me if my understanding is wrong.

Following is the Callback Sequence (from 6.1 kernel) that gets executed upon calling pci_alloc_irq_vectors:
pci_alloc_irq_vectors =>
 pci_alloc_irq_vectors_affinity =>
__pci_enable_msi_range =>
 pci_setup_msi_context =>
 pcim_setup_msi_release =>

devm_add_action(&dev->dev, pcim_msi_release, dev);

Inside pcim_msi_release: (called since pcim_enable_device is used)
pci_free_irq_vectors(dev);

>From this sequence, it seemed like, kernel takes care of freeing irq and calling pci_free_irq_vectors is not required. 

Thanks,
Tharun Kumar P