https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=191265
Bug ID: 191265
Summary: [patch] uart(4) punishes UARTs for being too fast
Product: Base System
Version: 11.0-CURRENT
Hardware: Any
OS: Any
Status: Needs Triage
Severity: Affects Only Me
Priority: ---
Component: kern
Assignee: freebsd-bugs@FreeBSD.org
Reporter: sh...@freebsd.org
Created attachment 144015
--> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=144015&action=edit
Fix for discarding data when internal buffer full.
For NS8250 family UARTs, svn 120146 -
http://svnweb.freebsd.org/base?view=revision&revision=120146 - made a change to
flush the UART if the kernel buffers are full. The commit message suggests
this is because of how the read loop was structured.
However, this change mad it so that if the internal FreeBSD buffer is full, it
will drop all pending data... effectively punishing devices for having too much
data buffered. At least one network exposed UART is capable of this.
The attached patch doesn't clear the interrupt if the rx buffer is full by
checking the buffer has space before reading LSR.
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