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From: Josh Triplett <josh@joshtriplett.org>
To: "Maciej W. Rozycki" <macro@orcam.me.uk>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jiri Slaby <jirislaby@kernel.org>
Cc: Anders Blomdell <anders.blomdell@control.lth.se>,
	linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org,
	stable@vger.kernel.org
Subject: Re: [PATCH 0/2] serial: 8250: Let drivers request full 16550A feature probing
Date: Sat, 17 Sep 2022 16:00:59 +0100	[thread overview]
Message-ID: <0B189972-4FD8-4245-BF2F-ADEAB18AAAE0@joshtriplett.org> (raw)
In-Reply-To: <alpine.DEB.2.21.2209162317180.19473@angie.orcam.me.uk>

On September 17, 2022 11:07:18 AM GMT+01:00, "Maciej W. Rozycki" <macro@orcam.me.uk> wrote:
>Hi,
>
> A recent change has added a SERIAL_8250_16550A_VARIANTS option, which 
>lets one request the 8250 driver not to probe for 16550A device features 
>so as to reduce the driver's device startup time in virtual machines.  
>This has turned out problematic to a more recent update for the OxSemi 
>Tornado series PCIe devices, whose new baud rate generator handling code 
>actually requires switching hardware into the enhanced mode for correct 
>operation, which actually requires 16550A device features to have been 
>probed for.
>
> This small patch series fixes the issue by letting individual device 
>subdrivers to request full 16550A device feature probing by means of a 
>flag regardless of the SERIAL_8250_16550A_VARIANTS setting chosen.
>
> The changes have been verified with an OXPCIe952 device, in the native 
>UART mode and a 64-bit RISC-V system as well as in the legacy UART mode 
>and a 32-bit x86 system.

Seems reasonable to me, as long as the flag is only set by drivers that know they've found their hardware.


  parent reply	other threads:[~2022-09-17 15:01 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-09-17 10:07 [PATCH 0/2] serial: 8250: Let drivers request full 16550A feature probing Maciej W. Rozycki
2022-09-17 10:07 ` [PATCH 1/2] " Maciej W. Rozycki
2022-09-19  4:42   ` Jiri Slaby
2022-09-19  8:18     ` Maciej W. Rozycki
2022-09-19 10:49       ` Jiri Slaby
2022-09-20 23:35         ` Maciej W. Rozycki
2022-09-17 10:07 ` [PATCH 2/2] serial: 8250: Request full 16550A feature probing for OxSemi PCIe devices Maciej W. Rozycki
2022-09-19  4:44   ` Jiri Slaby
2022-09-19  8:23     ` Maciej W. Rozycki
2022-09-20 23:35       ` Maciej W. Rozycki
2022-09-17 15:00 ` Josh Triplett [this message]
2022-09-18  8:26   ` [PATCH 0/2] serial: 8250: Let drivers request full 16550A feature probing Maciej W. Rozycki

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