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Scanning: explain ipp-usb scan issue and how driverless scanning works

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Zdenek Dohnal 2022-05-10 08:50:20 +02:00
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commit 930e7400de
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4
modules/ROOT/pages/_partials/con_cups-known-issues.adoc
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@ -174,7 +174,9 @@ Devices which require a HP close source binary plugin need to have plugin instal
=== USB printer/scanner doesn't work due a conflict on USB port
*ipp-usb* daemon keeps the USB port of IPP-over-USB device opened for any possible IPP communication in the future, which blocks the port for other drivers (f.e. HPLIP, gutenprint, sane-backends...). For printers the solution is to _uninstall the queue with the driver_ and start using the one from *ipp-usb* (as a xref:cups-terminology.adoc#_temporary_print_queues[CUPS temporary queue] or install a permanent one - the default device uri is `ipp://localhost:60000/ipp/print`). In case of scanners *sane-airscan* automatically picks up the virtual device from *ipp-usb* if the device is capable of using WSD or eSCL protocols.
*ipp-usb* daemon keeps the USB port of IPP-over-USB device opened for any possible IPP communication in the future, which blocks the port for other drivers (f.e. HPLIP, gutenprint, sane-backends...). For printers the solution is to _uninstall the queue with the driver_ and start using the one from *ipp-usb* (as a xref:cups-terminology.adoc#_temporary_print_queues[CUPS temporary queue] or install a permanent one - the default device uri is `ipp://localhost:60000/ipp/print`).
In case of scanners *sane-airscan* automatically picks up the virtual device from *ipp-usb* if the device is capable of using WSD or eSCL protocols. However, if the scanner had been supported by classic scanner driver such as hplip or sane-backends and is now claimed by *ipp-usb* because it supports *IPP-over-USB* driverless standard, the old scanner is still shown, but it won't work for scanning due USB conflict. It happens because classic backends just list any device which they can find on USB interfaces and matches the description the backend supports, but backends don't check whether they actually can communicate with the device until they try to open the USB port for scanning process itself. This becomes a problem for scanning applications, which automatically choose the previous scanner as a default choice for scanning (such as _Simple Scan_) - users have to pick a driverless scanner from the list of available scanners before they scan.
If *ipp-usb* created device doesn't match your use case (the options you use are missing, the device doesn't work even if it is IPP-over-USB supported), please report the issue together with logs from [filename]`/var/log/ipp-usb/` directory at https://bugzilla.redhat.com[bugzilla]. *ipp-usb* itself supports quirks, which allows you to set the daemon to ignore your device and you can switch back to a classic driver. See [command]`man ipp-usb`.

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modules/ROOT/pages/_partials/con_cups-terminology-for-printing-and-scanning.adoc
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@ -80,4 +80,4 @@ The classic scanning works via backends, which are binaries for communication wi
The driverless scanning uses sane-escl (not built in Fedora) and sane-airscan backends for communicating with newer devices. Those newer devices usually support eSCL (based on AirScan protocol by Apple) or WSD (Web Services for Devices by Microsoft), which _sane-airscan_ is able to use.
Regarding USB scanning, it has the same requirement as printing. The device must support IPP over USB and 'ipp-usb' package must be installed to get driverless scanning via USB.
Regarding USB scanning, it has the same requirement as printing. The device must support IPP over USB driverless standard and _ipp-usb_ package must be installed to get driverless scanning via USB - the package is required because it creates a driverless interface over USB interface which _sane-airscan_ uses for driverless communication with device.