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Fri, 04 Dec 2020 04:26:15 -0800 (PST) Date: Fri, 4 Dec 2020 13:26:14 +0100 From: Thierry Reding To: Sowjanya Komatineni Cc: Mark Brown , jonathanh@nvidia.com, robh+dt@kernel.org, linux-spi@vger.kernel.org, linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org Subject: Re: [PATCH v1 3/7] spi: qspi-tegra: Add support for Tegra210 QSPI controller Message-ID: References: <1606857168-5839-1-git-send-email-skomatineni@nvidia.com> <1606857168-5839-4-git-send-email-skomatineni@nvidia.com> <20201202172721.GL5560@sirena.org.uk> <2257bc33-80ef-a6d8-8542-480defa32937@nvidia.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="dMt5SDLPoOEwNGde" Content-Disposition: inline In-Reply-To: <2257bc33-80ef-a6d8-8542-480defa32937@nvidia.com> User-Agent: Mutt/2.0.2 (d9268908) (2020-11-20) Precedence: bulk List-ID: X-Mailing-List: linux-spi@vger.kernel.org --dMt5SDLPoOEwNGde Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Wed, Dec 02, 2020 at 11:17:18AM -0800, Sowjanya Komatineni wrote: > On 12/2/20 9:27 AM, Mark Brown wrote: > > On Tue, Dec 01, 2020 at 01:12:44PM -0800, Sowjanya Komatineni wrote: [...] > > > +static int tegra_qspi_setup(struct spi_device *spi) > > > +{ > > > + if (cdata && cdata->tx_clk_tap_delay) > > > + tx_tap = cdata->tx_clk_tap_delay; > > > + if (cdata && cdata->rx_clk_tap_delay) > > > + rx_tap = cdata->rx_clk_tap_delay; > > > + tqspi->def_command2_reg = QSPI_TX_TAP_DELAY(tx_tap) | > > > + QSPI_RX_TAP_DELAY(rx_tap); > > > + tegra_qspi_writel(tqspi, tqspi->def_command2_reg, QSPI_COMMAND2); > > The setup for one device shouldn't be able to affect the operation of > > another, already running, device so either these need to be configured > > as part of the controller probe or these configurations need to be > > deferred until we're actually doing a transfer. > We will only have 1 device on QSPI as we only support single chip select. Even so we could make the driver operate as if there were multiple devices. This has the advantage of setting a better example for someone who might be reading this code as reference, and it might come in handy if for whatever reason we ever end up with a QSPI controller that does support multiple chip selects. If that's overly complicated, maybe a compromise would be to document very explicitly that this only works because Tegra QSPI supports a single chip select? 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