On Thu, 27 Jun 2013 at 07:17, Greg KH wrote:
On Wed, Jun 26, 2013 at 12:03:23PM +0200, Reinhard Max wrote:
OTOH, why should a driver impose such a limit at all [...]
Because that's the way the driver has successfully worked for the
past 10+ years?
Well, this particular part was added less than four years ago[1],
apparently based on experiments that a single person did on a single
device (a PL2303HX as per the comment). I've contacted him to find out
if he still has access to that device and could double-check his
findings.
Meanwhile I found "Datasheets" dating from 2004 for the PL2303X[2] to
2012 for newer variants like PL2303HXD[3] and PL2303SA[4] that have
sentences like the following in their "Introduction" chapter:
"The flexible baud rate generator of PL-2303HXD could be programmed
to generate any rate between 75 bps to 12M bps."
"The flexible baud rate generator of PL2303SA also could be
programmed to generate any rate between 75 bps to 115 kbps by driver
customization."
But there are also datasheets for the original PL2303 and PL2303H from
2002[5] and 2005[6] that do not contain such a statement.
Again, remember, this driver was created by reverse engineering the
protocol, the fact that it works at all is amazing.
I am very well aware of that.
But still, if the worst thing that might happen when an invalid data
rate is selected is that 9600 baud is used instead, I'd prefer that
over a driver that by trying to be clever keeps me from using data
rates that my hardware would perfectly support.
Things would of course be different if setting unsupported baud rates
caused the hardware to crash, but I think there is no indication of
this being the case for any member of the PL2303 family.
cu
Reinhrd
[1] https://git.kernel.org/cgit/linux/kernel/git/gregkh/usb.git/commit?id=25b8286805e856c8c7fda127018e31032c918015
[2] http://prolificusa.com/pdf/PL-2303XA.pdf
[3] http://prolificusa.com/files/ds_pl2303HXD_v1.4.3.pdf
[4] http://prolificusa.com/files/DS_PL2303SA_d20120504.pdf
[5] http://www.digchip.com/datasheets/download_datasheet.php?id=1751150&part-number=PL2303
[6] http://www.electronicaestudio.com/docs/PL2303.pdf
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