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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49268ff9f40sm69047585e9.6.2026.06.26.03.55.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 26 Jun 2026 03:55:14 -0700 (PDT) Date: Fri, 26 Jun 2026 11:55:12 +0100 From: David Laight To: Michal Pecio 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: <20260626115512.5add7b23@pumpkin> In-Reply-To: <20260626105723.42972329.michal.pecio@gmail.com> 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> <20260626105723.42972329.michal.pecio@gmail.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) 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 10:57:23 +0200 Michal Pecio wrote: > 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. Clearly the only hardware testing was 'does it work with 32bit windows' :-) David > > Regards, > Michal