Re: [PATCH v2 09/14] rt2x00: rt2x00pci: set PCI MWI only if supported

From: John Crispin <john@phrozen.org>
To: Daniel Golle <daniel@makrotopia.org>,
	Stanislaw Gruszka <sgruszka@redhat.com>
Cc: linux-wireless@vger.kernel.org,
	Johannes Berg <johannes@sipsolutions.net>,
	roman@advem.lv, michel.stempin@wanadoo.fr, c.mignanti@gmail.com,
	evaxige@qq.com, Kalle Valo <kvalo@codeaurora.org>,
	Felix Fietkau <nbd@nbd.name>, Gabor Juhos <juhosg@openwrt.org>
Subject: Re: [PATCH v2 09/14] rt2x00: rt2x00pci: set PCI MWI only if supported
Date: Tue, 17 Jan 2017 08:34:44 +0100	[thread overview]
Message-ID: <ae4e2f18-b60d-4e28-5c31-014da951ab30@phrozen.org> (raw)
In-Reply-To: <20170117015653.GF1912@makrotopia.org>


On 17/01/2017 02:56, Daniel Golle wrote:
> On Mon, Jan 16, 2017 at 11:08:57AM +0100, Stanislaw Gruszka wrote:
>> On Mon, Jan 16, 2017 at 04:06:25AM +0100, Daniel Golle wrote:
>>> From: Claudio Mignanti <c.mignanti@gmail.com>
>>>
>>> This is needed for devices without support for PCI MWI. See also
>>> https://dev.openwrt.org/changeset/21850
>>>
>>> Signed-off-by: Daniel Golle <daniel@makrotopia.org>
>>> ---
>>>  drivers/net/wireless/ralink/rt2x00/rt2x00pci.c | 2 ++
>>>  1 file changed, 2 insertions(+)
>>>
>>> diff --git a/drivers/net/wireless/ralink/rt2x00/rt2x00pci.c b/drivers/net/wireless/ralink/rt2x00/rt2x00pci.c
>>> index eb6dbcd4fddf..4becfeb75ba8 100644
>>> --- a/drivers/net/wireless/ralink/rt2x00/rt2x00pci.c
>>> +++ b/drivers/net/wireless/ralink/rt2x00/rt2x00pci.c
>>> @@ -94,8 +94,10 @@ int rt2x00pci_probe(struct pci_dev *pci_dev, const struct rt2x00_ops *ops)
>>>  
>>>  	pci_set_master(pci_dev);
>>>  
>>> +#ifdef CONFIG_PCI_SET_MWI
>>>  	if (pci_set_mwi(pci_dev))
>>>  		rt2x00_probe_err("MWI not available\n");
>>> +#endif
>>
>> There is no CONFIG_PCI_SET_MWI in the kernel. This patch is either not
>> needed (pci subsystem has own PCI_DISABLE_MWI define) or wrong (we
>> should not call this function for some devices).
> 
> Apparently we thus never enabled MWI on PCI devices. John Crispin has
> started to investigate why this patch was needed in first place, see
> http://lists.infradead.org/pipermail/lede-dev/2017-January/005400.html
> 
> I suggest to drop it entirely until we figure out why it wasn't safe to
> use MWI at least on some platforms. Once we know more there might be
> a follow-up to selectively have the precompiler skip pci_set_mwi in
> case we really still need to do this.
> Aparently this was originally related to a compiler error on Kernel
> 2.6.30 when trying to build for Rt305x WiSoC platforms (which simply
> do not have any PCI bus and probably explicite support for SoC devices
> wasn't implemented in rt2x00 at the time).
> 
> 

here is the original thread related to this patch

http://rt2x00.serialmonkey.com/pipermail/users_rt2x00.serialmonkey.com/2012-November/012227.html

	John

> Cheers
> 
> 
> Daniel
> 
>>
>> Stanislaw