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Wed, 22 Nov 2023 21:55:13 +0000 Date: Wed, 22 Nov 2023 13:55:06 -0800 From: Vikram Garhwal To: Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= Cc: qemu-devel@nongnu.org, Anton Kochkov , Francisco Iglesias , Jason Wang , Pavel Pisa , Vikram Garhwal , Qiang Liu Subject: Re: [PATCH-for-8.2 v2 1/2] hw/net/can/xlnx-zynqmp: Avoid underflow while popping TX FIFOs Message-ID: References: <20231119225102.49227-1-philmd@linaro.org> <20231119225102.49227-2-philmd@linaro.org> Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20231119225102.49227-2-philmd@linaro.org> X-ClientProxiedBy: BYAPR21CA0006.namprd21.prod.outlook.com (2603:10b6:a03:114::16) To MW3PR12MB4409.namprd12.prod.outlook.com (2603:10b6:303:2d::23) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: MW3PR12MB4409:EE_|DS7PR12MB5765:EE_ X-MS-Office365-Filtering-Correlation-Id: 05236b69-02df-4ec3-eaff-08dbeba5b496 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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envelope-from=vikram.garhwal@amd.com; helo=NAM04-BN8-obe.outbound.protection.outlook.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.058, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Hi, On Sun, Nov 19, 2023 at 11:51:01PM +0100, Philippe Mathieu-Daudé wrote: > Per https://docs.xilinx.com/r/en-US/ug1085-zynq-ultrascale-trm/Message-Format > > Message Format > > The same message format is used for RXFIFO, TXFIFO, and TXHPB. > Each message includes four words (16 bytes). Software must read > and write all four words regardless of the actual number of data > bytes and valid fields in the message. > > There is no mention in this reference manual about what the > hardware does when not all four words are written. To fix the > reported underflow behavior when DATA2 register is written, > I choose to fill the data with the previous content of the > ID / DLC / DATA1 registers, which is how I expect hardware > would do. > > Note there is no hardware flag raised under such condition. > > Reported-by: Qiang Liu > Fixes: 98e5d7a2b7 ("hw/net/can: Introduce Xilinx ZynqMP CAN controller") > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1425 > Signed-off-by: Philippe Mathieu-Daudé > Francisco Iglesias > --- > hw/net/can/xlnx-zynqmp-can.c | 49 +++++++++++++++++++++++++++++++++--- > 1 file changed, 46 insertions(+), 3 deletions(-) > > diff --git a/hw/net/can/xlnx-zynqmp-can.c b/hw/net/can/xlnx-zynqmp-can.c > index e93e6c5e19..58938b574e 100644 > --- a/hw/net/can/xlnx-zynqmp-can.c > +++ b/hw/net/can/xlnx-zynqmp-can.c > @@ -434,6 +434,51 @@ static bool tx_ready_check(XlnxZynqMPCANState *s) > return true; > } > > +static void read_tx_frame(XlnxZynqMPCANState *s, Fifo32 *fifo, uint32_t *data) > +{ > + unsigned used = fifo32_num_used(fifo); > + bool is_txhpb = fifo == &s->txhpb_fifo; > + > + assert(used > 0); > + used %= CAN_FRAME_SIZE; > + > + /* > + * Frame Message Format > + * > + * Each frame includes four words (16 bytes). Software must read and write > + * all four words regardless of the actual number of data bytes and valid > + * fields in the message. > + * If software misbehave (not writting all four words), we use the previous %s/writting/writing > + * registers content to initialize each missing word. > + */ > + if (used > 0) { > + /* ID, DLC, DATA1 missing */ Code is correct but i feel This comment is confusing. ID is missing for sure if user > 0 but same is not the case for DLC and DATA1. > + data[0] = s->regs[is_txhpb ? R_TXHPB_ID : R_TXFIFO_ID]; > + } else { > + data[0] = fifo32_pop(fifo); > + } > + if (used == 1 || used == 2) { > + /* DLC, DATA1 missing */ Same here DLC is missing for sure but DATA1 is not for used == 2. > + data[1] = s->regs[is_txhpb ? R_TXHPB_DLC : R_TXFIFO_DLC]; > + } else { > + data[1] = fifo32_pop(fifo); > + } > + if (used == 1) { > + /* DATA1 missing */ May be we remove all these individual comments and write a common comment before the first check(if(used > 0)). Something like this: /* * If used is 1 then ID, DLC and DATA1 are missing. * * if used is 2 then ID and DLC are missing. * * if used is 3 then only ID is missing. */ Code looks correct to me. So, With above minor changes in code comments: Reviewed-by: Vikram Garhwal > + data[2] = s->regs[is_txhpb ? R_TXHPB_DATA1 : R_TXFIFO_DATA1]; > + } else { > + data[2] = fifo32_pop(fifo); > + } > + /* DATA2 triggered the transfer thus is always available */ > + data[3] = fifo32_pop(fifo); > + > + if (used) { > + qemu_log_mask(LOG_GUEST_ERROR, > + "%s: Incomplete CAN frame (only %u/%u slots used)\n", > + TYPE_XLNX_ZYNQMP_CAN, used, CAN_FRAME_SIZE); > + } > +} > + > static void transfer_fifo(XlnxZynqMPCANState *s, Fifo32 *fifo) > { > qemu_can_frame frame; > @@ -451,9 +496,7 @@ static void transfer_fifo(XlnxZynqMPCANState *s, Fifo32 *fifo) > } > > while (!fifo32_is_empty(fifo)) { > - for (i = 0; i < CAN_FRAME_SIZE; i++) { > - data[i] = fifo32_pop(fifo); > - } > + read_tx_frame(s, fifo, data); > > if (ARRAY_FIELD_EX32(s->regs, STATUS_REGISTER, LBACK)) { > /* > -- > 2.41.0 >