Hi Weijie,
On Thu, 29 Oct 2020 at 03:47, Weijie Gao weijie.gao@mediatek.com wrote:
On Mon, 2020-10-26 at 22:51 -0600, Simon Glass wrote:
Hi Weijie,
On Fri, 16 Oct 2020 at 01:36, Weijie Gao weijie.gao@mediatek.com wrote:
This patch adds uart support for MediaTek MT7620 and earlier SoCs.
The UART used by MT7620 is incompatible with the ns16550a driver. All registers of this UART have different addresses. A special 16-bit register for Divisor Latch is used to set the baudrate instead of the original two 8-bit registers (DLL and DLM).
The driver can be built without DM which is useful for tiny SPL.
Signed-off-by: Weijie Gao weijie.gao@mediatek.com
drivers/serial/Kconfig | 20 ++ drivers/serial/Makefile | 1 + drivers/serial/serial.c | 2 + drivers/serial/serial_mt7620.c | 350 +++++++++++++++++++++++++++++++++ 4 files changed, 373 insertions(+) create mode 100644 drivers/serial/serial_mt7620.c
Why do you need to build without DM? We have of-platdata which provides for smaller images. What is the SRAM size available?
Actually it's the total size (spl+u-boot-lzma.img) that matters. mt7620_rfb_defconfig is configured to be compatible with the original u-boot from MTK SDK, and the maximum size is 192KiB.
What is lzma.img ?
Currently without SPL_DM, the final image u-boot-with-spl.bin is about 170KiB, the u-boot-spl.bin is only 20KiB.
That is definitely huge.
If SPL_DM is enabled, the total size is 189KiB, which is very close to the limit 192KiB, and the size of spl is almost doubled, 39KiB. (Without DM, only serial_mt7620 is needed. However with DM, both serial_mt7620, clk-mt7620 and misc are needed)
Considering that we may still add some feature to mt7620_rfb_defconfig in the future, only 3KiB left is not enough. Building without DM is apparently better.
I believe using of-platdata can only reduce few KiBs of SPL, because the DM itself is the largest overhead.
That's not my experience. The core DM overhead is fairly small, perhaps 3-4KB. The device tree itself is typically at least another 3KB, depending on how many nodes you mark for inclusion in SPL.
With of-platdata the overhead of DM is not that terrible. You can see some stats here:
http://u-boot.10912.n7.nabble.com/RFC-PATCH-v2-0-3-RFC-tiny-dm-Proposal-for-...
Regards, SImon