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Wed, 26 Nov 2025 08:45:32 -0800 (PST) Message-ID: <97d8026590edd4911eb03d775b10f14ecc60ba6e.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 17:45:25 +0100 In-Reply-To: References: <20251126090759.4042709-1-flavra@baylibre.com> <562c2b30820d083ff0b5e04ac176ed66c0064363.camel@baylibre.com> Organization: BayLibre Content-Type: multipart/signed; micalg="pgp-sha512"; protocol="application/pgp-signature"; boundary="=-EKhWMttrzvdjrYMHMS/T" 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 --=-EKhWMttrzvdjrYMHMS/T Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, 2025-11-26 at 18:25 +0200, Andy Shevchenko wrote: > On Wed, Nov 26, 2025 at 01:08:23PM +0100, Francesco Lavra wrote: > > 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: >=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 /d= ev/ttyTHS0, 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 these 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). Thi= s driver 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 perfor= mance. > > > > +=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 ma= y use 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 baudrat= e and better performance. > >=20 > > 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. >=20 > OK. But this is not the case for Tegra234? Or is it and it uses DMA for > UART? Yes, that is the case, Tegra234 has just a different DMA controller (TEGRA186_GPC_DMA), which is used by the UART driver as long as the relevant device tree node properties are in place. --=-EKhWMttrzvdjrYMHMS/T Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part -----BEGIN PGP SIGNATURE----- iQGzBAABCgAdFiEEhleFT5U73KMewxTm7fE7c86UNl8FAmknLqUACgkQ7fE7c86U Nl8Xgwv/QpYpkRG+HQ/Gpx+YaFVbMHzzufhGg9iGhGsQMNjKUORsUJSpogB8gp7H geennZAn9E02VtI5uXq+VxVbJmkaQhKvOYEjy7VmR9UPS9Ka9i6npGp/b6ISvFs+ PU7T5GNKq2g9Tse+qv1E50pdrDEiExmWy0EW1MpO9up5E5Fl0mu25Uhmweu6HfiD o8lHHkrQEfU5qbExsxKHz3gWPN66rTl7lBtN4M60VslEbrLW3LSFX/h+/t9qLUsO CbGXyFyJfefK7fEA6c7K9SFO3qiXK9xKoh/hlzIiXaNJAawUaAEfyJ5jbeRMfHks Nxk7JXBOMVFRO/qgEU4PafoRvS0NINb5U69lFp3BWkOT0ib4vv3s/VLHyT2vDbts EG9VFYEupTpb9qmDqyiYLAR8kHwffiRL54mZ83pXaFCK/2sUPhX+ZPN4WRduHuSQ +9uOLYZ1tXcvbWtnTa4krZoq2PjFugGqZpR7NhELwtbKVb/zZOgdVU0WUoQE8/2K ZiV5IUTu =L3lp -----END PGP SIGNATURE----- --=-EKhWMttrzvdjrYMHMS/T--