Hi Bin, Simon,
On 7/16/2019 11:21 AM, Bin Meng wrote:
+Simon,
Hi Alex,
On Mon, Jul 15, 2019 at 7:45 PM Alexandru Marginean
<alexandru.margin...@nxp.com> wrote:
On 7/13/2019 7:02 AM, Bin Meng wrote:
Hi Alex,
On Fri, Jul 12, 2019 at 10:21 PM Alex Marginean
<alexandru.margin...@nxp.com> wrote:
This driver is used for MDIO muxes driven over I2C. This is currently
used on Freescale LS1028A QDS board, on which the physical MDIO MUX is
controlled by an on-board FPGA which in turn is configured through I2C.
Signed-off-by: Alex Marginean <alexm.ossl...@gmail.com>
---
Depends on https://patchwork.ozlabs.org/project/uboot/list/?series=119124
drivers/net/Kconfig | 8 +++
drivers/net/Makefile | 1 +
drivers/net/mdio_mux_i2c_reg.c | 108 +++++++++++++++++++++++++++++++++
3 files changed, 117 insertions(+)
create mode 100644 drivers/net/mdio_mux_i2c_reg.c
diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
index 4d85fb1716..93535f7acb 100644
--- a/drivers/net/Kconfig
+++ b/drivers/net/Kconfig
@@ -595,4 +595,12 @@ config FSL_ENETC
This driver supports the NXP ENETC Ethernet controller found on some
of the NXP SoCs.
+config MDIO_MUX_I2C_REG
I don't see current Linux upstream has any I2CREG support. I believe
you will upstream the Linux support too?
Linux support is somewhat different so we won't have the same driver and
binding there. The main difference is that Linux has the concept of a
mux controller, independent of the type of bus it muxes. I didn't add
this to U-Boot, not yet at least.
This specific MDIO mux would be driven in Linux by a pair of devices:
- a mux controller with bindings defined by reg-mux.txt [1], this one
implements the select function,
- MDIO mux as a client of the controller, defined by
mdio-mux-multiplexer.txt [2], which deals with the MDIO specific side of
things.
Thanks for the detailed explanations! I thought people wanted to have
exact the same DT bindings as Linux so that we can sync-up upstream
kernel DT changes to U-Boot. That's why at first I checked whether
kernel has such bindings in place.
In U-Boot I picked up the relevant properties from the two bindings, the
MDIO mux device in U-Boot is supposed to implement select like a generic
Linux MUX, while the uclass code deals with MDIO.
I noticed U-Boot already has an I2C MUX class, along the lines of the
MDIO one, I'm not sure if it's useful enough to introduce a new class of
MUX controllers and then make all other kind of muxes depend on it. For
now at least the U-Boot mux drivers are simple enough and the extra
class wouldn't help much.
The other difference is that in Linux the mux controller is driven by
the 'MMIO register bitfield-controlled multiplexer driver' [3], which is
not I2C specific. It is built on top of regmap which I also think is a
bit too much for U-Boot. For the U-Boot driver I just called I2C API
directly and in that context it made sense to add I2C to the driver
name, but there won't be an equivalent I2C based driver for Linux.
For your current implementation I believe that's OK, at least it is
verified on LS1028. But there must be a reason that Linux kernel chose
a DT that is different. I suspect the usage of kernel DT makes us stay
future-proof.
Having a generic mux controller that's independent of the muxed bus has
its merit, of course. Right now the API that a MDIO MUX must implement
in U-Boot has just a _select function, which, by itself, has not direct
relation to MDIO and could be used for other buses. So mux controllers
could work in U-Boot, at least to keep U-Boot in sync with Linux.
I'm not sure about reg/mmio-mux. Those work in Linux because of regmap
and layers that abstract the underlying bus which I think are a bit too
much for U-Boot. Of course without that abstraction we can't use
"reg-mux" or "mdio-mux-multiplexer" compatibility strings for the more
specific devices and drivers in U-Boot.
I'd really appreciate some feedback on this. I think the fairly simple
approach in U-Boot is good enough, but I'm open to suggestions.
I am open on this topic too. Agreed that for U-Boot we always want a
simple implementation for device drivers. I am adding Simon for his
opinion on this topic as well.
Thank you, let's see what Simon thinks about this.
Alex
[1]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/mux/reg-mux.txt
[2]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/net/mdio-mux-multiplexer.txt
[3]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/mux/mmio.c
Regards,
Bin
_______________________________________________
U-Boot mailing list
U-Boot@lists.denx.de
https://lists.denx.de/listinfo/u-boot
_______________________________________________
U-Boot mailing list
U-Boot@lists.denx.de
https://lists.denx.de/listinfo/u-boot
