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

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Message-ID: <447b30df-cb9e-cfaf-6381-0a1c426fa57c@oth-regensburg.de>
Date:   Sat, 17 Jul 2021 14:44:43 +0200
From:   Ralf Ramsauer <ralf.ramsauer@...-regensburg.de>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
CC:     Jiri Slaby <jirislaby@...nel.org>, <linux-serial@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [EXT] Re: [PATCH v1 3/4] serial: 8250_pci: Always try MSI/MSI-X



On 16/07/2021 19:27, Andy Shevchenko wrote:
> On Fri, Jul 16, 2021 at 05:27:36PM +0200, Ralf Ramsauer wrote:
>> On 16/07/2021 17:01, Andy Shevchenko wrote:
>>> On Fri, Jul 16, 2021 at 4:07 PM Ralf Ramsauer
>>> <ralf.ramsauer@...-regensburg.de> wrote:
>>>> On 14/07/2021 15:35, Andy Shevchenko wrote:
>>>>> On Wed, Jul 14, 2021 at 3:56 PM Ralf Ramsauer
>>>>> <ralf.ramsauer@...-regensburg.de> wrote:
>>>>>> On 14/07/2021 08:54, Jiri Slaby wrote:
>>>>>>> On 13. 07. 21, 12:40, Andy Shevchenko wrote:
>>>>>
>>>>>>> Hmm, have you checked the commit which introduced the whitelist?
>>>>>>>
>>>>>>>     Nevertheless, this needs to handled with care: while many 8250 devices
>>>>>>>     actually claim to support MSI(-X) interrupts it should not be
>>>>>>> enabled be
>>>>>>>     default. I had at least one device in my hands with broken MSI
>>>>>>>     implementation.
>>>>>>>
>>>>>>>     So better introduce a whitelist with devices that are known to support
>>>>>>>     MSI(-X) interrupts. I tested all devices mentioned in the patch.
>>>>>>>
>>>>>>>
>>>>>>> You should have at least CCed the author for an input.
>>>>>>
>>>>>> Yep, back then I was testing three different 8250 pci cards. All of them
>>>>>> claimed to support MSI, while one really worked with MSI, the one that I
>>>>>> whitelisted. So I thought it would be better to use legacy IRQs as long
>>>>>> as no one tested a specific card to work with MSI.
>>>>>
>>>>> Can you shed a light eventually what those cards are?
>>>
>>>> So I found a no-name el-cheapo card that has some issues with MSI:
>>>
>>> Win Chip Head (WCH)
>>>
>>>> 18:00.0 Serial controller: Device 1c00:3253 (rev 10) (prog-if 05 [16850])
> 
> Thank you!
> 
> One more thing, ist it possible to see entire PCI configuration space (w/ or
> w/o MSI, I don't think it matters)? Something like
> 
> 	`lspci -nk -vvv -xxx -s 18:0`
> 
> to run.
> 
> (I believe there are a lot of 0xff bytes)

Find it attached, w/ MSI+. Not that many, only the 0xffs for the MSI
mask, afaict.

  Ralf

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