Re: [PATCH v2 1/3] tty: serial: introduce transmit helper generators
From: Jiri Slaby
Date: Fri Sep 02 2022 - 06:24:22 EST
On 02. 09. 22, 12:22, Ilpo Järvinen wrote:
On Thu, 1 Sep 2022, Jiri Slaby wrote:
Many serial drivers do the same thing:
* send x_char if set
* keep sending from the xmit circular buffer until either
- the loop reaches the end of the xmit buffer
- TX is stopped
- HW fifo is full
* check for pending characters and:
- wake up tty writers to fill for more data into xmit buffer
- stop TX if there is nothing in the xmit buffer
The only differences are:
* how to write the character to the HW fifo
* the check of the end condition:
- is the HW fifo full?
- is limit of the written characters reached?
So unify the above into two helper generators:
* DEFINE_UART_PORT_TX_HELPER_LIMITED() -- it performs the above taking
the written characters limit into account, and
* DEFINE_UART_PORT_TX_HELPER() -- the same as above, except it only
checks the HW readiness, not the characters limit.
The HW specific operations (as stated as "differences" above) are passed
as arguments to the macros. They are:
* tx_ready() -- returns true if HW can accept more data.
* put_char() -- write a character to the device.
* tx_done() -- when the write loop is done, perform arbitrary action
before potential invocation of ops->stop_tx() happens.
Note that the above macros are generators. This means the code is
generated in place and the above 3 arguments are "inlined". I.e. no
added penalty by generating call instructions for every single
character. Nor any indirect calls. (As in previous versions of this
patchset.)
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
Notes:
[v2] instead of a function (uart_port_tx_limit()) in serial_core,
generate these in-place using macros. Thus eliminating "call"
penalty.
Documentation/driver-api/serial/driver.rst | 3 +
include/linux/serial_core.h | 86 ++++++++++++++++++++++
2 files changed, 89 insertions(+)
diff --git a/Documentation/driver-api/serial/driver.rst b/Documentation/driver-api/serial/driver.rst
index 23c6b956cd90..25775bf1fcc6 100644
--- a/Documentation/driver-api/serial/driver.rst
+++ b/Documentation/driver-api/serial/driver.rst
@@ -78,6 +78,9 @@ Other functions
uart_get_lsr_info uart_handle_dcd_change uart_handle_cts_change
uart_try_toggle_sysrq uart_get_console
+.. kernel-doc:: include/linux/serial_core.h
+ :identifiers: DEFINE_UART_PORT_TX_HELPER_LIMITED DEFINE_UART_PORT_TX_HELPER
+
Other notes
-----------
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index 6e4f4765d209..715778160ae1 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -646,6 +646,92 @@ struct uart_driver {
void uart_write_wakeup(struct uart_port *port);
+#define __DEFINE_UART_PORT_TX_HELPER(name, port, ch, tx_ready, put_char, \
+ tx_done, for_test, for_post, ...) \
+unsigned int name(struct uart_port *port __VA_OPT__(,) __VA_ARGS__) \
+{ \
+ struct circ_buf *xmit = &port->state->xmit; \
+ unsigned int pending; \
+ u8 ch; \
+ \
+ for (; (for_test) && (tx_ready); (for_post), port->icount.tx++) { \
+ * The functions in parameters shall be designed as follows:
+ * * **tx_ready(port):** the function shall return true if the HW can accept
+ * more data to be sent. This function can be %NULL, which means the HW is
+ * always ready.
So if tx_ready can be NULL, how does that for() loop above work??
Sorry, the docs is wrong (corresponded to v1). I fixed it locally already:
https://git.kernel.org/pub/scm/linux/kernel/git/jirislaby/linux.git/commit/?h=devel&id=989c488c69faf2987648e09358c79d75b4a3b5c7
thanks,
--
js
suse labs