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Availability of TRB's is calculated using dwc3_calc_trbs_left(), which determines total available TRB's based on the HWO bit set in a TRB. In the present code, __dwc3_prepare_one_trb() is called with a TRB which needs to be prepared for transfer. This __dwc3_prepare_one_trb() calls dwc3_calc_trbs_left() to determine total available TRBs and set IOC bit if the total available TRBs are zero. Since the present working TRB (which is passed as an argument to __dwc3_prepare_one_trb() ) doesn't yet have the HWO bit set before calling dwc3_calc_trbs_left(), there are chances that dwc3_calc_trbs_left() wrongly calculates this present working TRB as free(since the HWO bit is not yet set) and returns the total available TRBs as greater than zero (including the present working TRB). This could be a problem. This patch corrects the above mentioned problem in __dwc3_prepare_one_trb() by increementing the dep->trb_enqueue at the last (after preparing the TRB) instead of increementing at the start and setting the IOC bit only if the total available TRBs returned by dwc3_calc_trbs_left() is 1 . Since we are increementing the dep->trb_enqueue at the last, the present working TRB is also considered as available by dwc3_calc_trbs_left() and non zero value is returned . So, according to the modified logic, when the total available TRBs is equal to 1 that means the total available TRBs in the pool are 0. Signed-off-by: Anurag Kumar Vulisha <anurag.kumar.vulisha@xilinx.com> Reviewed-by: Thinh Nguyen <thinhn@synopsys.com> Tested-by: Tejas Joglekar <tejas.joglekar@synopsys.com> Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
To understand all the Linux-USB framework, you'll use these resources:
* This source code. This is necessarily an evolving work, and
includes kerneldoc that should help you get a current overview.
("make pdfdocs", and then look at "usb.pdf" for host side and
"gadget.pdf" for peripheral side.) Also, Documentation/usb has
more information.
* The USB 2.0 specification (from www.usb.org), with supplements
such as those for USB OTG and the various device classes.
The USB specification has a good overview chapter, and USB
peripherals conform to the widely known "Chapter 9".
* Chip specifications for USB controllers. Examples include
host controllers (on PCs, servers, and more); peripheral
controllers (in devices with Linux firmware, like printers or
cell phones); and hard-wired peripherals like Ethernet adapters.
* Specifications for other protocols implemented by USB peripheral
functions. Some are vendor-specific; others are vendor-neutral
but just standardized outside of the www.usb.org team.
Here is a list of what each subdirectory here is, and what is contained in
them.
core/ - This is for the core USB host code, including the
usbfs files and the hub class driver ("hub_wq").
host/ - This is for USB host controller drivers. This
includes UHCI, OHCI, EHCI, and others that might
be used with more specialized "embedded" systems.
gadget/ - This is for USB peripheral controller drivers and
the various gadget drivers which talk to them.
Individual USB driver directories. A new driver should be added to the
first subdirectory in the list below that it fits into.
image/ - This is for still image drivers, like scanners or
digital cameras.
../input/ - This is for any driver that uses the input subsystem,
like keyboard, mice, touchscreens, tablets, etc.
../media/ - This is for multimedia drivers, like video cameras,
radios, and any other drivers that talk to the v4l
subsystem.
../net/ - This is for network drivers.
serial/ - This is for USB to serial drivers.
storage/ - This is for USB mass-storage drivers.
class/ - This is for all USB device drivers that do not fit
into any of the above categories, and work for a range
of USB Class specified devices.
misc/ - This is for all USB device drivers that do not fit
into any of the above categories.