On Mon, Mar 28, 2022 at 11:36:46AM -0400, Sean Anderson wrote:
On 3/28/22 2:35 AM, Simon Glass wrote:
Hi Sean,
On Tue, 22 Mar 2022 at 15:00, Sean Anderson sean.anderson@seco.com wrote:
This adds a serial driver which uses semihosting calls to read and write to the host's console. For convenience, if CONFIG_DM_SERIAL is enabled, we will instantiate a serial driver. This allows users to enable this driver (which has no physical device) without modifying their device trees or board files. We also implement a non-DM driver for SPL, or for much faster output in U-Boot proper.
There are three ways to print to the console:
Method Baud ================== ===== smh_putc in a loop 170 smh_puts 1600 smh_write with :tt 20000 ================== =====
These speeds were measured using a 175 character message with a J-Link adapter. For reference, U-Boot typically prints around 2700 characters during boot on this board. There are two major factors affecting the speed of these functions. First, each breakpoint incurs a delay. Second, each debugger memory transaction incurs a delay. smh_putc has a breakpoint and memory transaction for every character. smh_puts has one breakpoint, but still has to use a transaction for every character. This is because we don't know the length up front, so OpenOCD has to check if each character is nul. smh_write has only one breakpoint and one memory transfer.
DM serial drivers can only implement a putc interface, so we are stuck with the slowest API. Non-DM drivers can implement puts, which is vastly more efficient. When the driver starts up, we try to open :tt. Since this is an extension, this may fail. If it does, we fall back to smh_puts. We don't check :semihosting-features, since there are nonconforming implementations (OpenOCD) which don't implement it (but *do* implement :tt).
Some semihosting implementations (QEMU) don't handle READC properly. To work around this, we try to use open/read (much like for stdin) if possible.
There is no non-blocking I/O available, so we don't implement pending. This will cause __serial_tstc to always return true. If CONFIG_SERIAL_RX_BUFFER is enabled, _serial_tstc will try and read characters forever. To avoid this, we depend on this config being disabled.
Signed-off-by: Sean Anderson sean.anderson@seco.com
(no changes since v2)
Changes in v2:
- Fix baud numbers being off by 10
- Fix typos in commit message
- Rename non-DM driver struct to match format of other drivers
drivers/serial/Kconfig | 22 +++++ drivers/serial/Makefile | 1 + drivers/serial/serial.c | 2 + drivers/serial/serial_semihosting.c | 147 ++++++++++++++++++++++++++++ include/serial.h | 1 + 5 files changed, 173 insertions(+) create mode 100644 drivers/serial/serial_semihosting.c
Reviewed-by: Simon Glass sjg@chromium.org
But please can we drop the non-DM support?
Unfortunately, Layerscape does not support DM serial. I tried converting it, but I ran into some unusual aborts. At the moment, I don't have time to debug things further. And I thought that non-DM serial was ok for SPL?
It is OK for SPL, and it needs migration for non-SPL. Can you make another thread with your conversion-that-fails for layerscape please?