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

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Date:   Fri, 16 Jul 2021 20:27:34 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Ralf Ramsauer <ralf.ramsauer@...-regensburg.de>
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 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)

-- 
With Best Regards,
Andy Shevchenko