From mboxrd@z Thu Jan 1 00:00:00 1970 From: =?UTF-8?q?Marc=20Mar=C3=AD?= Subject: [PATCH v3] QEMU fw_cfg DMA interface documentation Date: Fri, 18 Sep 2015 10:59:27 +0200 Message-ID: <1442566767-5222-1-git-send-email-markmb@redhat.com> References: <1442566703-5091-1-git-send-email-markmb@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <1442566703-5091-1-git-send-email-markmb@redhat.com> Sender: linux-kernel-owner@vger.kernel.org To: linux-kernel@vger.kernel.org Cc: Drew , Stefan Hajnoczi , Kevin O'Connor , Gerd Hoffmann , Laszlo , Arnd Bergmann , Rob Herring , Mark Rutland , Alexander Graf , devicetree@vger.kernel.org, =?UTF-8?q?Marc=20Mar=C3=AD?= List-Id: devicetree@vger.kernel.org Add fw_cfg DMA interface specfication in the fw_cfg documentation. Signed-off-by: Marc Mar=C3=AD --- Documentation/devicetree/bindings/arm/fw-cfg.txt | 49 ++++++++++++++++= +++++++- 1 file changed, 48 insertions(+), 1 deletion(-) diff --git a/Documentation/devicetree/bindings/arm/fw-cfg.txt b/Documen= tation/devicetree/bindings/arm/fw-cfg.txt index 953fb64..ba6945e 100644 --- a/Documentation/devicetree/bindings/arm/fw-cfg.txt +++ b/Documentation/devicetree/bindings/arm/fw-cfg.txt @@ -45,6 +45,51 @@ blob to be read from the data register has size 4, a= nd it is to be interpreted as a uint32_t value in little endian byte order. The current value (corresponding to the above outer protocol) is zero. =20 +If bit 1 of the feature bitmap is set, the DMA interface is present. T= his +can be used through the 64-bit wide address register. + +The address register is in big-endian format. The value for the regist= er is 0 +at startup and after an operation. A write to the lower half triggers = an +operation. This means, that operations with 32-bit addresses can be tr= iggered +with just one write, whereas operations with 64-bit addresses can be t= riggered +with one 64-bit write or two 32-bit writes, starting with the higher p= art. + +In this register, the physical address of a FWCfgDmaAccess structure i= n RAM +should be written. This is the format of the FWCfgDmaAccess structure: + +typedef struct FWCfgDmaAccess { + uint32_t control; + uint32_t length; + uint64_t address; +} FWCfgDmaAccess; + +The fields of the structure are in big endian mode, and the field at t= he lowest +address is the "control" field. + +The "control" field has the following bits: + - Bit 0: Error + - Bit 1: Read + - Bit 2: Skip + - Bit 3: Select. The upper 16 bits are the selected index. + +When an operation is triggered, if the "control" field has bit 3 set, = the +upper 16 bits are interpreted as an index of a firmware configuration = item. +This has the same effect as writing the selector register. + +If the "control" field has bit 1 set, a read operation will be perform= ed. +"length" bytes for the current selector and offset will be copied into= the +physical RAM address specified by the "address" field. + +If the "control" field has bit 2 set (and not bit 1), a skip operation= will be +performed. The offset for the current selector will be advanced "lengt= h" bytes. + +To check result, read the "control" field: + error bit set -> something went wrong. + all bits cleared -> transfer finished successfully. + otherwise -> transfer still in progress (doesn't happen + today due to implementation not being asyn= c, + but may in the future). + The guest kernel is not expected to use these registers (although it i= s certainly allowed to); the device tree bindings are documented here be= cause this is where device tree bindings reside in general. @@ -56,6 +101,8 @@ Required properties: - reg: the MMIO region used by the device. * Bytes 0x0 to 0x7 cover the data register. * Bytes 0x8 to 0x9 cover the selector register. + * With DMA interface enabled: Bytes 0xc to 0x13 cover the DMA addres= s + register. * Further registers may be appended to the region in case of future = interface revisions / feature bits. =20 @@ -66,7 +113,7 @@ Example: #address-cells =3D <0x2>; =20 fw-cfg@9020000 { + reg =3D <0x0 0x9020000 0x0 0x14>; compatible =3D "qemu,fw-cfg-mmio"; - reg =3D <0x0 0x9020000 0x0 0xa>; }; }; --=20 2.4.3