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[79.185.222.186]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-54d6e5cf922sm921663e87.149.2025.04.21.02.49.46 (version=TLS1_2 cipher=AES128-SHA bits=128/128); Mon, 21 Apr 2025 02:49:47 -0700 (PDT) Date: Mon, 21 Apr 2025 11:49:43 +0200 From: =?UTF-8?B?TWljaGHFgg==?= Pecio To: Greg KH Cc: Laurent Pinchart , Hans de Goede , Mauro Carvalho Chehab , linux-media@vger.kernel.org, linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org Subject: Re: [PATCH] media: uvcvideo: Support large SuperSpeedPlus isochronous endpoints Message-ID: <20250421114943.085160c6@foxbook> In-Reply-To: <2025042101-coyness-vitality-e636@gregkh> References: <20250421095951.1e63824e@foxbook> <2025042101-coyness-vitality-e636@gregkh> Precedence: bulk X-Mailing-List: linux-usb@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Mon, 21 Apr 2025 10:51:38 +0200, Greg KH wrote: > On Mon, Apr 21, 2025 at 09:59:51AM +0200, Michal Pecio wrote: > > USB 3.1 increased maximum isochronous bandwidth to 96KB per > > interval, too much for 16 bits and the SuperSpeed Endpoint > > Companion descriptor. A new SuperSpeedPlus Isochronous Endpoint > > Companion descriptor was introduced to encode such bandwidths, see > > spec sections 9.6.7, 9.6.8. > > > > Support the descriptor with code based on > > xhci_get_max_esit_payload() and widen all 'psize' variables to 32 > > bits. Subsequent calculations are 32 bit already and not expected > > to overflow, so this change ought to suffice for proper alt setting > > selection on USB 3.x Gen 2 devices. > > > > Signed-off-by: Michal Pecio > > --- > > > > This change appears to be a strict necessity for supporting USB3 > > Gen2 isochronous devices meaningfully. Whether it's sufficient I > > don't know, I don't have such HW. No regression seen on High Speed > > and SuperSpeed. > > If you don't have the hardware, why make this change? Because it's an obvious and easily removed limitation, and may be the only thing missing in uvcvideo to support such hardware. I saw it when investigating a related SuperSpeed problem earlier. If media believes that more is needed, or if there is objection to such changes based on spec alone then fine, at least the patch is out there for anyone wondering why things aren't working. > > drivers/media/usb/uvc/uvc_ > > This line looks odd, because: > > > drivers/media/usb/uvc/uvc_driver.c | 2 +- > > drivers/media/usb/uvc/uvc_video.c | 13 +++++++++---- > > drivers/media/usb/uvc/uvcvideo.h | 4 ++-- > > 3 files changed, 12 insertions(+), 7 deletions(-) > > Only 3 files were changed. What went wrong? Sorry, some editing mistake.