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[2003:e4:1f1c:800:f22f:74ff:fe1f:3a53]) by smtp.gmail.com with ESMTPSA id n4-20020a5099c4000000b00501cc88b3adsm4982468edb.46.2023.03.23.02.50.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 23 Mar 2023 02:50:18 -0700 (PDT) Date: Thu, 23 Mar 2023 10:50:17 +0100 From: Thierry Reding To: Akhil R Cc: Jonathan Hunter , "christian.koenig@amd.com" , "digetx@gmail.com" , Laxman Dewangan , "linux-i2c@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-tegra@vger.kernel.org" , "sumit.semwal@linaro.org" , "wsa@kernel.org" Subject: Re: [PATCH v3] i2c: tegra: Share same DMA channel for RX and TX Message-ID: References: <20230322102413.52886-1-akhilrajeev@nvidia.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="/U2W7SI2pG14y3lP" Content-Disposition: inline In-Reply-To: User-Agent: Mutt/2.2.9 (2022-11-12) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --/U2W7SI2pG14y3lP Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Mar 23, 2023 at 09:26:00AM +0000, Akhil R wrote: > > On 22/03/2023 12:00, Akhil R wrote: > > >> On 22/03/2023 10:24, Akhil R wrote: > > >>> Allocate only one DMA channel for I2C and share it for both TX and = RX > > >>> instead of using two different DMA hardware channels with the same > > >>> slave ID. Since I2C supports only half duplex, there is no impact on > > >>> perf with this. > > >>> > > >>> Signed-off-by: Akhil R > > >> > > >> Just to confirm. This impacts all Tegra devices from Tegra20 to the > > >> latest. Does this work for all Tegra and the different DMA controlle= rs > > >> that they have? > > >> > > > Yes, It should. I could see in the APB DMA driver that the same chann= el > > > could be used for TX and RX and the direction is configured only duri= ng > > > dma_prep_*() calls. > > > I did not test it on a Tegra with APB DMA, but since it works very si= milar > > > to GPC DMA there should not be any impact. > >=20 > >=20 > > OK. BTW, this does not apply cleanly on top of -next. It appears that > > this is based on top "i2c: tegra: Fix PEC support for SMBUS block read" > > and that one needs to be applied first. This can be avoided if you send > > as a series. > >=20 > Oh. Okay. I used 'git am --3way' when I tried, and the conflict went unno= ticed. > Shall I send a new version on top of -next? > The two patches were added in different contexts and that=E2=80=99s why I= did not > combine them as a series. It's usually best to combine them in a series even if they are in slightly different contexts. This is especially true if they cause conflicts between one another. If you send them as a series, you can resolve the conflicts yourself (you may not even have conflicts locally if you create the patches in the same branch), but if you send them separately the maintainer will end up having to resolve the conflicts (or apply in the right order). It's best if you resolve the conflicts because you know better than the maintainer (usually) or specify any dependencies to make it easier for the maintainer to do the right thing. But again, in the vast majority of cases, it's best to combine all the work on one driver in a single series before sending out. 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