linux-kernel - Re: [PATCH v4 22/30] PCI/Parisc: Use pci_scan_root

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Date:	Tue, 3 Mar 2015 17:31:44 +0800
From:	Yijing Wang <wangyijing@...wei.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
CC:	Jiang Liu <jiang.liu@...ux.intel.com>, <linux-pci@...r.kernel.org>,
	Yinghai Lu <yinghai@...nel.org>,
	<linux-kernel@...r.kernel.org>,
	Marc Zyngier <marc.zyngier@....com>,
	<linux-arm-kernel@...ts.infradead.org>,
	Russell King <linux@....linux.org.uk>, <x86@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Tony Luck <tony.luck@...el.com>, <linux-ia64@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	"Guan Xuetao" <gxt@...c.pku.edu.cn>, <linux-alpha@...r.kernel.org>,
	<linux-m68k@...ts.linux-m68k.org>, Liviu Dudau <liviu@...au.co.uk>,
	"Arnd Bergmann" <arnd@...db.de>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	"Yijing Wang" <wangyijing0307@...il.com>,
	"James E.J. Bottomley" <jejb@...isc-linux.org>,
	<linux-parisc@...r.kernel.org>
Subject: Re: [PATCH v4 22/30] PCI/Parisc: Use pci_scan_root_bus() for simplicity

On 2015/3/3 11:24, Bjorn Helgaas wrote:
> On Thu, Feb 26, 2015 at 04:12:16PM +0800, Yijing Wang wrote:
>> From: Yijing Wang <wangyijing0307@...il.com>
> 
> When you write subject lines, I think it's friendly to run
> "git log --oneline" on the file you're changing, and make yours
> match the previous ones.
> 
>   $ git log --oneline drivers/parisc/dino.c
>   3f05536d226d PCI/Parisc: Use pci_scan_root_bus() for simplicity
>   3335f75a8877 parisc: dino: fix %d confusingly prefixed with 0x in format string
>   3fad9b8d597f drivers/parisc: Use printf extension %pR for struct resource
>   0fe763c570ad Drivers: misc: remove __dev* attributes.
>   0b79ca2a800d parisc/PCI: Use list_for_each_entry() for bus->devices traversal
>   30aa80da43a5 parisc/PCI: register busn_res for root buses
>   ...
> 
> Yours doesn't match any of them, but "parisc/PCI" seems the best match.

OK, I will refresh the title, sorry.

> 
>> Now pci_bus_add_devices() has been ripped out
>> from pci_scan_root_bus(), we could use pci_scan_root_bus()
>> instead of pci_create_root_bus() + pci_scan_child_bus()
>> for simplicity. We could also remove the pci bus
>> resource(dino_current_bus,255) and pci_bus_update_busn_res_end(),
>> because pci_scan_root_bus() would do the same thing.
>>
>> Signed-off-by: Yijing Wang <wangyijing@...wei.com>
>> CC: "James E.J. Bottomley" <jejb@...isc-linux.org>
>> CC: linux-parisc@...r.kernel.org
>> ---
>>  drivers/parisc/dino.c    |   11 ++---------
>>  drivers/parisc/lba_pci.c |    7 ++-----
>>  2 files changed, 4 insertions(+), 14 deletions(-)
>>
>> diff --git a/drivers/parisc/dino.c b/drivers/parisc/dino.c
>> index a0580af..e5ee339 100644
>> --- a/drivers/parisc/dino.c
>> +++ b/drivers/parisc/dino.c
>> @@ -977,15 +977,11 @@ static int __init dino_probe(struct parisc_device *dev)
>>  	if (dino_dev->hba.gmmio_space.flags)
>>  		pci_add_resource(&resources, &dino_dev->hba.gmmio_space);
>>  
>> -	dino_dev->hba.bus_num.start = dino_current_bus;
>> -	dino_dev->hba.bus_num.end = 255;
>> -	dino_dev->hba.bus_num.flags = IORESOURCE_BUS;
>> -	pci_add_resource(&resources, &dino_dev->hba.bus_num);
> 
> I know pci_scan_root_bus() does default to bus 0-255, but I don't really
> like that behavior, and I think it's a bug for drivers like this to rely on
> that.  The PCI core has no way to discover the actual bus number range, and
> the only reason it supplies a default is because it was inconvenient to
> change all the callers.  The host bridge driver is the only code that has
> any chance of discovering and/or configuring the correct range.
> 
> So I think it's more correct to leave the existing code here, even though
> this code is is likely incorrect.  At least then if we trip over an issue
> with the bus range being incorrect, it will be clear that the fix should
> be in dino.c rather than the PCI core.

OK, I would keep this code here, thanks!

> 
> .
> 


-- 
Thanks!
Yijing

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