Sorry I'm rather late to the Linux game. I have searched the archive for references to csfo and cache but I have not found anything to explain the issue I am looking at, though there are discussions in the immediate area.

If I am referring to outdated information please let me know and I can then get back to my vendor to straighten things out.

From my reading the csfo word has been placed in the first word of the vendor specific area of the IDENTIFY DEVICE information.

The t13.org document "Mandatory IDENTIFY DEVICE and IDENTIFY PACKET DEVICE fields" defines words 129-159 as vendor specific. The latest release would appear to be http://www.t13.org/technical/e00159r3.pdf and I have not found any discussion which would render this document obsolete. There are documents relating to modifications in unrelated areas, but I could not find any referring to word 129. Perhaps I'm just not looking in the right place?

In include/linux/hdreg.h word 129 is defined as csfo

   unsigned short  csfo;        /*  (word 129)
                    * current set features options
                    * 15:4    reserved
                    *  3:    auto reassign
                    *  2:    reverting
                    *  1:    read-look-ahead
                    *  0:    write cache
                    */

which is then used to switch cache operations in drivers/ide/ide-disk.c as follows

       /* Cache enabled ? */
       if (drive->id->csfo & 1)
           drive->wcache = 1;


So that means that the first word of the vendor specific code is being used to select whether cache operations are enabled.


In the particular case of the flash IDE drive I am using that first word is the day number of the date, so for devices built on odd days the cache is enabled and for even days disabled. The device has no cache.

So has my vendor missed the repurposing of word 129? Can anyone point me to documentation which defines it as csfo?

I apologize if this is an ignorant question, but t13.org seem to hold the standards for these drives so that's where I went for information.

Thank you
Chris
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