From mboxrd@z Thu Jan 1 00:00:00 1970 From: Simon Glass Date: Thu, 29 Oct 2020 08:30:40 -0600 Subject: [PATCH 08/18] serial: add uart driver for MediaTek MT7620 SoC In-Reply-To: <1603964837.18736.26.camel@mcddlt001> References: <1602833759-19379-1-git-send-email-weijie.gao@mediatek.com> <1603964837.18736.26.camel@mcddlt001> Message-ID: List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: u-boot@lists.denx.de Hi Weijie, On Thu, 29 Oct 2020 at 03:47, Weijie Gao 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 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 > > > --- > > > 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-using-driver-model-in-SPL-td418552.html Regards, SImon