linux-kernel - Re: [PATCH v3 2/3] uio_pci_generic: add MSI/MSI-X support

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Message-ID: <56123E29.4020202@cloudius-systems.com>
Date:	Mon, 5 Oct 2015 12:08:57 +0300
From:	Vlad Zolotarov <vladz@...udius-systems.com>
To:	Stephen Hemminger <stephen@...workplumber.org>
Cc:	linux-kernel@...r.kernel.org, mst@...hat.com, hjk@...sjkoch.de,
	corbet@....net, gregkh@...uxfoundation.org,
	bruce.richardson@...el.com, avi@...udius-systems.com,
	gleb@...udius-systems.com, alexander.duyck@...il.com
Subject: Re: [PATCH v3 2/3] uio_pci_generic: add MSI/MSI-X support



On 10/05/15 11:41, Stephen Hemminger wrote:
> On Sun,  4 Oct 2015 23:43:17 +0300
> Vlad Zolotarov <vladz@...udius-systems.com> wrote:
>
>> +static int setup_maps(struct pci_dev *pdev, struct uio_info *info)
>> +{
>> +	int i, m = 0, p = 0, err;
>> +	static const char * const bar_names[] = {
>> +		"BAR0",	"BAR1",	"BAR2",	"BAR3",	"BAR4",	"BAR5",
>> +	};
>> +
>> +	for (i = 0; i < ARRAY_SIZE(bar_names); i++) {
>> +		unsigned long start = pci_resource_start(pdev, i);
>> +		unsigned long flags = pci_resource_flags(pdev, i);
>> +		unsigned long len = pci_resource_len(pdev, i);
>> +
>> +		if (start == 0 || len == 0)
>> +			continue;
>> +
>> +		if (flags & IORESOURCE_MEM) {
>> +			void __iomem *addr;
>> +
>> +			if (m >= MAX_UIO_MAPS)
>> +				continue;
>> +
>> +			addr = ioremap(start, len);
>> +			if (addr == NULL) {
>> +				err = -EINVAL;
>> +				goto fail;
>> +			}
>> +
>> +			info->mem[m].name = bar_names[i];
>> +			info->mem[m].addr = start;
>> +			info->mem[m].internal_addr = addr;
>> +			info->mem[m].size = len;
>> +			info->mem[m].memtype = UIO_MEM_PHYS;
>> +			++m;
>> +		} else if (flags & IORESOURCE_IO) {
>> +			if (p >= MAX_UIO_PORT_REGIONS)
>> +				continue;
>> +
>> +			info->port[p].name = bar_names[i];
>> +			info->port[p].start = start;
>> +			info->port[p].size = len;
>> +			info->port[p].porttype = UIO_PORT_X86;
>> +			++p;
>> +		}
>> +	}
>> +
>> +	return 0;
>> +fail:
>> +	for (i = 0; i < m; i++) {
>> +		iounmap(info->mem[i].internal_addr);
>> +		info->mem[i].internal_addr = NULL;
>> +	}
>> +
>> +	return err;
>> +
> I wonder do we really have to setup all the BAR's in uio_pci_generic?
> The DPDK code works with uio_pci_generic already, and it didn't setup the BAR's.

DPDK never used uio_pci_generic with MSI-X support so far and all MSI-X 
capable UIO DPDK drivers like igb_uio and your newly proposed uio_msi do 
map them all.
U also mentioned in the other thread that virtio requires portio bars too.
The thing is that generally bars are needed for programming the device 
therefore it's logical to have them exposed. In general different 
devices have different registers layout therefore a general driver may 
not know which bar exactly is going to be required for a specific device 
and for a specific usage. That's why I think that "map them all" 
approach is rather generic and appropriate. However if there are other 
motives not to do so that I'm missing, pls., let me know.

thanks,
vlad

> One possible issue is that without that maybe kernel would not know about the
> region used for MSI-X vectors table.

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