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[ Upstream commit 9d6a54c1430647355a5e23434881b2ca3d192b48 ] The OUT endpoint normally blocks (NAK) subsequent packets when a short packet was received and returns an incomplete queue entry to the gadget driver. Thereby the gadget driver can detect a short packet when reading queue entries with a length that is not equal to a multiple of packet size. The start_queue() function enables receiving OUT packets regardless of the content of the OUT FIFO. This results in a race: With the current code, it's possible that the "!ep->is_in && (readl(&ep->regs->ep_stat) & BIT(NAK_OUT_PACKETS))" test in start_dma() will fail, then a short packet will be received, and then start_queue() will call stop_out_naking(). That's what we don't want (OUT naking gets turned off while there is data in the FIFO) because then the next driver request might receive a mixture of old and new packets. With the patch, this race can't occur because the FIFO's state is tested after we know that OUT naking is already turned on, and OUT naking is stopped only when both of the conditions are met. This ensures that all received data is delivered to the gadget driver, which can detect a short packet now before new packets are appended to the last short packet. Acked-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Guido Kiener <guido.kiener@rohde-schwarz.com> Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com> Signed-off-by: Sasha Levin (Microsoft) <sashal@kernel.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.