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Rozycki" , Greg Kroah-Hartman , Jiri Slaby CC: Anders Blomdell , linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: =?US-ASCII?Q?Re=3A_=5BPATCH_0/2=5D_serial=3A_8250=3A_Let_driv?= =?US-ASCII?Q?ers_request_full_16550A_feature_probing?= In-Reply-To: References: Message-ID: <0B189972-4FD8-4245-BF2F-ADEAB18AAAE0@joshtriplett.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On September 17, 2022 11:07:18 AM GMT+01:00, "Maciej W=2E Rozycki" wrote: >Hi, > > A recent change has added a SERIAL_8250_16550A_VARIANTS option, which=20 >lets one request the 8250 driver not to probe for 16550A device features= =20 >so as to reduce the driver's device startup time in virtual machines=2E = =20 >This has turned out problematic to a more recent update for the OxSemi=20 >Tornado series PCIe devices, whose new baud rate generator handling code= =20 >actually requires switching hardware into the enhanced mode for correct= =20 >operation, which actually requires 16550A device features to have been=20 >probed for=2E > > This small patch series fixes the issue by letting individual device=20 >subdrivers to request full 16550A device feature probing by means of a=20 >flag regardless of the SERIAL_8250_16550A_VARIANTS setting chosen=2E > > The changes have been verified with an OXPCIe952 device, in the native= =20 >UART mode and a 64-bit RISC-V system as well as in the legacy UART mode= =20 >and a 32-bit x86 system=2E Seems reasonable to me, as long as the flag is only set by drivers that kn= ow they've found their hardware=2E