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[83.28.44.19]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49268fd9e77sm58423035e9.4.2026.06.26.01.57.25 (version=TLS1_2 cipher=AES128-SHA bits=128/128); Fri, 26 Jun 2026 01:57:26 -0700 (PDT) Date: Fri, 26 Jun 2026 10:57:23 +0200 From: Michal Pecio To: David Laight Cc: Xincheng Zhang , cyrozap@gmail.com, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org, mathias.nyman@intel.com Subject: Re: [PATCH] usb: xhci-pci: Disable 64-bit DMA for VIA VL805 Message-ID: <20260626105723.42972329.michal.pecio@gmail.com> In-Reply-To: <20260626090615.616666b4@pumpkin> References: <20260623121847.53749028.michal.pecio@gmail.com> <20260624070612.337013-1-zhangxincheng@ultrarisc.com> <20260625020421.2e577a94.michal.pecio@gmail.com> <178235378952.3114334.15752812276771065417.b4-reply@b4> <20260625191852.0a8d511c.michal.pecio@gmail.com> <20260626090615.616666b4@pumpkin> Precedence: bulk X-Mailing-List: linux-kernel@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 Fri, 26 Jun 2026 09:06:15 +0100, David Laight wrote: > Can you do a read-back of one of the control registers that contains > an address - if you are lucky the high bits will return zero. > That might let the generic code enforce a limit. Interesting idea, but nope. My VL805 with 36 bit 013600 firmware is set up with 37 bit DMA mask right now. MMIO registers read: DCBAAP_LOW = 0xffffe000 DCBAAP_HIGH = 0x0000001f IR0_ERSTBA_LOW = 0xfffee000 IR0_ERSTBA_HIGH = 0x0000001f IR0_ERDP_LOW = 0xffff4018 IR0_ERDP_HIGH = 0x0000001f Nothing hints that the chip will truncate this to 36 bits when DMA-ing. We learn about it when it happens. Regards, Michal