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Wed, 26 Nov 2025 04:08:29 -0800 (PST) Message-ID: <562c2b30820d083ff0b5e04ac176ed66c0064363.camel@baylibre.com> Subject: Re: [PATCH] serial: tegra: remove Kconfig dependency on APB DMA controller From: Francesco Lavra To: Andy Shevchenko Cc: Greg Kroah-Hartman , Jiri Slaby , Kartik Rajput , Geert Uytterhoeven , Wolfram Sang , Robert Marko , Thierry Bultel , Douglas Anderson , linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org Date: Wed, 26 Nov 2025 13:08:23 +0100 In-Reply-To: References: <20251126090759.4042709-1-flavra@baylibre.com> Organization: BayLibre Content-Type: multipart/signed; micalg="pgp-sha512"; protocol="application/pgp-signature"; boundary="=-4UsuA/CWlgnfn7hIJ4In" User-Agent: Evolution 3.46.4-2 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 --=-4UsuA/CWlgnfn7hIJ4In Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, 2025-11-26 at 13:20 +0200, Andy Shevchenko wrote: > On Wed, Nov 26, 2025 at 10:07:59AM +0100, Francesco Lavra wrote: > > This driver runs also on SoCs without a Tegra20 APB DMA controller > > (e.g. > > Tegra234). > > Remove the Kconfig dependency on TEGRA20_APB_DMA, and remove reference > > to > > the APB DMA controller from the Kconfig help text. >=20 > ... >=20 > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0help > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 Support for the = on-chip UARTs on the NVIDIA Tegra series SOCs > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 providing /dev/t= tyTHS0, 1, 2, 3 and 4 (note, some machines > > may not > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 provide all of t= hese ports, depending on how the serial port > > -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 are enabled). This dr= iver uses the APB DMA to achieve higher > > baudrate > > -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 and better performanc= e. > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 are enabled). >=20 > I think this removes a good piece of information. Perhaps rephrase? >=20 > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 This driver may us= e the APB DMA when available to achieve > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 higher baudrate an= d better performance. I think this sentence would make it sound like the driver performs better if the APB DMA controller is available, but in reality the driver just uses the generic DMA API like most serial drivers, and there is nothing APB- specific in it. If another DMA controller (e.g. GPC on Tegra234) is available instead of the APB one, the serial peripheral will be just as fast. --=-4UsuA/CWlgnfn7hIJ4In Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part -----BEGIN PGP SIGNATURE----- iQGzBAABCgAdFiEEhleFT5U73KMewxTm7fE7c86UNl8FAmkm7bcACgkQ7fE7c86U Nl+z/gwAmiaXnYGPOKC8sRI8pyITLU0osYVW+668wjvfdv8+jjBhN5SYA2bqqVP7 LbVe24AjIPaeWQCIPlRvROxUWF3CkCVHN6j7izYtGDJkISFv1FxsH3jVZGLH620b DWJzrgPAfxyk3ZIzV3caYHwwkwU447NRli+eu2MRQz0DJhesr4eG8RcsCARx7oJB wxTvLAUAi2lLOzCIw2MBaAOR2UUmEWHSUEDBrHRh03p3yxicL6c73iWBFn3A+U08 xMdRxghYvk9k60JIVtsXlVX/KuOmhT7gyP5eObvNzhm0fJ9i0F8ldHxMyvy/TyMP do/r9iMlcHFNkNFwdbVH6KRKouePuQ9HBgiKBQwMHRQWCPrcc5WSzvGrN286gjSK jDiEV7feaPRuq1ve0f1B3vo3PHcDNhKHa8p/MAalKLn8M90RPd3jhQHUwN3p2eDZ c5+KSDX6+izS25EZGXa/YT0ehRC6HGaRbXWilTNab5HvzHjG5tl1jN9tx/RqyyKD U6U8CYkV =7XrJ -----END PGP SIGNATURE----- --=-4UsuA/CWlgnfn7hIJ4In--