On Mon, Jan 14, 2013 at 02:11:31PM +0100, Philip Oberstaller wrote: > Hi, > > I'm writing a driver for the Exar's XR20M1280 SPI-based serial port > using kernel version 3.4.17. We can't take drivers for older kernel versions, why not write it for 3.8 and then backport it when finished? > If a string, which is considerably longer than the driver's internal buffer > (512 bytes), is written with printf/fprintf to the dedicated port, then the > function call hangs after the driver's write_room function returns zero, > which happens when the driver's internal buffer is temporarily full. > I would have expected that the TTY layer or the libc implementation of > printf would requery write_room automatically and thus would notice > after a while that there is space again, but this doesn't seem to happen. That's right, the printf call should return a "short" write, but really, you should use write() and friends for tty ports, not fprintf, if at all possible to handle this type of error better. > Eventually the printf function returns after a very long timeout but without > that the remaining characters have been printed. > > I based my code mainly on the ifx6x60-driver and I looked at other similar > drivers as well, but I can't see that they are using a different strategy. > > In a dated driver book it was suggested that write_room and write should > always return at least one. I could use busy waiting in the write function > until there is space for at least one character, but I hope that there is > a better solution around?! I don't think so, sorry. > This e-mail communication contains information that is confidential > and may also be privileged. <snip> This type of footer really isn't good to have for public mailing list posts, it directly goes against the fact that you sent this to thousands of people in a public manner :) thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
