Hi Patrick,
On 03.09.2018 15:35, Patrick DELAUNAY wrote:
Hi Simon and Stefan,
Sorry for my late answer (I just come back from my summer holiday)
From: s...@google.com <s...@google.com> On Behalf Of Simon Glass
Sent: mercredi 8 août 2018 11:56
On 3 August 2018 at 05:38, Patrick Delaunay <patrick.delau...@st.com> wrote:
Add test to avoid access to rx buffer when this buffer is empty.
In this case directly call getc() function to avoid issue when tstc()
is not called.
Signed-off-by: Patrick Delaunay <patrick.delau...@st.com>
---
drivers/serial/serial-uclass.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/drivers/serial/serial-uclass.c
b/drivers/serial/serial-uclass.c index 321d23e..4121a37 100644
--- a/drivers/serial/serial-uclass.c
+++ b/drivers/serial/serial-uclass.c
@@ -228,6 +228,9 @@ static int _serial_getc(struct udevice *dev)
struct serial_dev_priv *upriv = dev_get_uclass_priv(dev);
char val;
+ if (upriv->rd_ptr == upriv->wr_ptr)
+ return __serial_getc(dev);
+
val = upriv->buf[upriv->rd_ptr++];
upriv->rd_ptr %= CONFIG_SERIAL_RX_BUFFER_SIZE;
--
2.7.4
Reviewed-by: Simon Glass <s...@chromium.org>
BTW I think the code in _serial_tstc() is wrong, or at least sub-optimal:
/* Read all available chars into the RX buffer */ while (__serial_tstc(dev)) {
upriv->buf[upriv->wr_ptr++] = __serial_getc(dev);
upriv->wr_ptr %= CONFIG_SERIAL_RX_BUFFER_SIZE; }
It should call serial_getc() until it returns -EAGAIN. There should be no need
to
call __serial_tstc() first,
This part had be added by Stefan Roese in
SHA1 3ca7a06afb7cbc867b7861a8b9aada74e5bbb559
But I check again the code, and I think the code is correct....
I really hope so. I did test this implementation quite heavily at
that time.
but I agree it is not optimal.
we can directly ops->getc(dev) and no more __serial_getc() or
__serial_tstc() :
the behavior don't change but the access to serial driver is reduced.
When no char is available, ops->getc witll return -EAGAIN
static int _serial_tstc(struct udevice *dev)
{
struct dm_serial_ops *ops = serial_get_ops(dev);
struct serial_dev_priv *upriv = dev_get_uclass_priv(dev);
int err;
/* Read all available chars into the RX buffer */
while(1) {
err = ops->getc(dev);
if (err < 0)
break;
upriv->buf[upriv->wr_ptr++] = err;
upriv->wr_ptr %= CONFIG_SERIAL_RX_BUFFER_SIZE;
}
return upriv->rd_ptr != upriv->wr_ptr ? 1 : 0;
}
If you are OK I will push a other patchset for these otpimisation.
I'm not 100% sure, if this new implementation is "better". Lets
compare the code:
Current version:
static int _serial_tstc(struct udevice *dev)
{
struct serial_dev_priv *upriv = dev_get_uclass_priv(dev);
/* Read all available chars into the RX buffer */
while (__serial_tstc(dev)) {
upriv->buf[upriv->wr_ptr++] = __serial_getc(dev);
upriv->wr_ptr %= CONFIG_SERIAL_RX_BUFFER_SIZE;
}
return upriv->rd_ptr != upriv->wr_ptr ? 1 : 0;
}
New version:
static int _serial_tstc(struct udevice *dev)
{
struct dm_serial_ops *ops = serial_get_ops(dev);
struct serial_dev_priv *upriv = dev_get_uclass_priv(dev);
int err;
/* Read all available chars into the RX buffer */
while(1) {
err = ops->getc(dev);
if (err < 0)
break;
upriv->buf[upriv->wr_ptr++] = err;
upriv->wr_ptr %= CONFIG_SERIAL_RX_BUFFER_SIZE;
}
return upriv->rd_ptr != upriv->wr_ptr ? 1 : 0;
}
The new version has more code and will most likely produce
a larger binary. You are removing the calls to the __foo()
functions - making the call chain a bit smaller. But this
will only affect the performance which is most likely negligible
in this case.
I any case, I don't object against any "optimizations" here.
But please make sure to test any changes very thorough - please
also on platforms with limited RX FIFO sizes.
Thanks,
Stefan
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