On 01/23/2015 04:31 AM, Paul Walmsley wrote:
+ Arto, Terje for comments on the host1x section
+ Stephen Warren for comments on the serial DT data
On Wed, 21 Jan 2015, Mark Rutland wrote:
As mentioned in my reply to the DT list patch [1], there are a couple of
bits I'd like to see cleaned up first, but in the meantime I have some
comments from my first pass of the dtsi below. Some of these may equally
apply to existing dts(i) files.
I see a few undocumented compatible strings (at least when comparing
against mainline). If there are other series or trees I should be
looking at, any pointers would be appreciated. If not, documentation
updates would be nice (checkpatch should complain otherwise).
On Fri, Jan 16, 2015 at 11:45:29AM +0000, Paul Walmsley wrote:
Add an initial device tree file for the Tegra132 SoC. The DT file is
based on arch/arm/boot/dts/tegra124.dtsi and
arch/arm/boot/dts/tegra114.dtsi, with the following significant
changes:
- Tegra132 uses a Denver CPU cluster rather than an ARMv7 CPU cluster
- Devices are arranged by bus, rather than in a flat topology
- No polling delays have been defined for the thermal zones. I don't
believe that this is a property of the SoC hardware, but rather of a
given use-case.
diff --git a/arch/arm64/boot/dts/tegra/tegra132.dtsi b/arch/arm64/boot/dts/tegra/tegra132.dtsi
+ /*
+ * There are two serial drivers: an 8250 based simple
+ * serial driver and an APB DMA based serial driver
+ * for higher baudrate and performance. To enable the
+ * 8250 based driver, the compatible string is
+ * "nvidia,tegra132-uart", "nvidia,tegra124-uart",
+ * "nvidia,tegra20-uart" and to enable the APB DMA
+ * based serial driver, the compatible string is
+ * "nvidia,tegra132-hsuart", "nvidia,tegra124-hsuart",
+ * "nvidia,tegra30-hsuart".
+ */
Is there any reason to continue with this split?
Surely if the only difference is DMA, the presence of dmas and dma-names
should be sufficient to get the driver to do the right thing, and if you
need to disable DMA for debugging that could be a command-line option.
I vaguely recall asking for the DMA support to be integrated into the
regular 8250 driver instead when the separate DMA-capable driver was
first added. I /think/ there was resistance to this because adding lots
of different SoC-specific ways to do DMA into the existing 8250 driver
would complicate it even more, and hence be unmaintainable.
I assume that reasoning is still valid.
Perhaps what we need is more fine-grained driver selection, not just
based on compatible value. Something like:
if compatible == nvidia,tegra20-uart:
if node.has_prop("enable-dma"):
driver = Tegra-specfic DMA capable UART driver
else:
driver = Common 8250 driver
Is that something that of_serial.c could/should be enhanced to do? That
said, the whole reasoning behind separate compatible properties before
was that compatible is supposed to "drive" driver selection. At least,
that's what I was told then.
Does the binding and/or driver support aliases so you can get consistent
numbering? It would be nice to have.
I believe either the serial core or serial driver(s) support DT aliases
now, yes.
Do these UARTs work with earlycon?
I do not know.
It would be nice to have a /chosen/stdout-path (ideally with rate) so as
to get output consistently without command line options being required.
Stephen Warren might be the best person to directly respond to these
issues. This is all legacy DT data from previous Tegra SoCs.
+ uarta: serial@0,70006000 {
+ compatible = "nvidia,tegra132-uart", "nvidia,tegra124-uart", "nvidia,tegra20-uart";
+ reg = <0x0 0x70006000 0x0 0x40>;
+ reg-shift = <2>;
+ interrupts = <GIC_SPI 36 IRQ_TYPE_LEVEL_HIGH>;
+ clocks = <&tegra_car TEGRA124_CLK_UARTA>;
+ resets = <&tegra_car 6>;
+ reset-names = "serial";
+ dmas = <&apbdma 8>, <&apbdma 8>;
+ dma-names = "rx", "tx";
+ status = "disabled";
+ };
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