linux-kernel - Re: [PATCH v1 3/4] serial: 8250

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Message-ID: <33767cf0-2104-d7aa-2da8-5a3f5f20a654@kernel.org>
Date:   Wed, 14 Jul 2021 09:58:52 +0200
From:   Jiri Slaby <jirislaby@...nel.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ralf Ramsauer <ralf.ramsauer@...-regensburg.de>
Subject: Re: [PATCH v1 3/4] serial: 8250_pci: Always try MSI/MSI-X

On 14. 07. 21, 8:54, Jiri Slaby wrote:
>> @@ -3994,14 +3982,9 @@ pciserial_init_ports(struct pci_dev *dev, const 
>> struct pciserial_board *board)
>>       if (board->flags & FL_NOIRQ) {
>>           uart.port.irq = 0;
>>       } else {
>> -        if (pci_match_id(pci_use_msi, dev)) {
>> -            dev_dbg(&dev->dev, "Using MSI(-X) interrupts\n");
>> -            pci_set_master(dev);
>> -            rc = pci_alloc_irq_vectors(dev, 1, 1, PCI_IRQ_ALL_TYPES);
>> -        } else {
>> -            dev_dbg(&dev->dev, "Using legacy interrupts\n");
>> -            rc = pci_alloc_irq_vectors(dev, 1, 1, PCI_IRQ_LEGACY);
>> -        }
>> +        pci_set_master(dev);
> 
> But bus mastering is not about MSIs. I *think* it's still OK, but you 
> need to document that in the commit log too.
> 
> Actually, why the commit which added this code turns on bus mastering?

Forget about this line, I wasn't woken enough. Of course, MSI (writes) 
to bus need bus mastering.

In any case, I'm still not sure what happens to devices which do not 
support MSI if we enable mastering on them?

-- 
js
suse labs