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Wed, 19 Apr 2023 10:20:14 +0000 Received: from nalasex01a.na.qualcomm.com (nalasex01a.na.qualcomm.com [10.47.209.196]) by NALASPPMTA01.qualcomm.com (8.17.1.5/8.17.1.5) with ESMTPS id 33JAKCT1004402 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 19 Apr 2023 10:20:12 GMT Received: from [10.50.61.92] (10.80.80.8) by nalasex01a.na.qualcomm.com (10.47.209.196) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.986.42; Wed, 19 Apr 2023 03:20:08 -0700 Message-ID: <44834c75-4db7-ec8a-9367-c6b83fa96b22@quicinc.com> Date: Wed, 19 Apr 2023 15:50:04 +0530 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.9.1 Subject: Re: [PATCH V22 2/3] misc: dcc: Add driver support for Data Capture and Compare unit(DCC) Content-Language: en-US To: Arnd Bergmann , Greg Kroah-Hartman CC: Andy Gross , Konrad Dybcio , Krzysztof Kozlowski , Bjorn Andersson , Rob Herring , Alex Elder , , , , , Sibi Sankar , Rajendra Nayak References: <2023041833-alienate-trash-f4da@gregkh> <50844899-b047-42fd-807a-db7136e5e590@app.fastmail.com> From: Souradeep Chowdhury In-Reply-To: <50844899-b047-42fd-807a-db7136e5e590@app.fastmail.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.80.80.8] X-ClientProxiedBy: nasanex01b.na.qualcomm.com (10.46.141.250) To nalasex01a.na.qualcomm.com (10.47.209.196) X-QCInternal: smtphost X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=5800 signatures=585085 X-Proofpoint-ORIG-GUID: N8MMapuDQ0UkoWEJyq6g7AB61zCCJioX X-Proofpoint-GUID: N8MMapuDQ0UkoWEJyq6g7AB61zCCJioX X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.254,Aquarius:18.0.942,Hydra:6.0.573,FMLib:17.11.170.22 definitions=2023-04-19_06,2023-04-18_01,2023-02-09_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 phishscore=0 lowpriorityscore=0 suspectscore=0 impostorscore=0 malwarescore=0 mlxlogscore=999 clxscore=1015 adultscore=0 spamscore=0 priorityscore=1501 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2303200000 definitions=main-2304190091 X-Spam-Status: No, score=-4.7 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,T_SCC_BODY_TEXT_LINE,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 4/19/2023 1:00 PM, Arnd Bergmann wrote: > On Wed, Apr 19, 2023, at 09:00, Souradeep Chowdhury wrote: >> On 4/18/2023 9:15 PM, Greg Kroah-Hartman wrote: >>> >>>> The following is the justification of using debugfs interface over the >>>> other alternatives like sysfs/ioctls >>>> >>>> i) As can be seen from the debugfs attribute descriptions, some of the >>>> debugfs attribute files here contains multiple arguments which needs to >>>> be accepted from the user. This goes against the design style of sysfs. >>>> >>>> ii) The user input patterns have been made simple and convenient in this >>>> case with the use of debugfs interface as user doesn't need to shuffle >>>> between different files to execute one instruction as was the case on >>>> using other alternatives. >>> >>> Why do you have debugfs and also a misc device? How are they related? >>> Why both? Why not just one? What userspace tools are going to use >>> either of these interfaces and where are they published to show how this >>> all was tested? >> >> DCC has two fundamental steps of usage:- >> >> 1.Configuring the register addresses on the dcc_sram which is done by >> user through the debugfs interface. For example:- >> >> echo R 0x10c004 > /sys/kernel/debug/dcc/../3/config >> >> Here we are configuring the register addresses for list 3, the 'R' >> indicates a read operation, so this register value will be read >> in case of a software trigger or kernel panic/watchdog bite and >> dumped into the dcc_sram. > > Can you describe why the register location needs to be > runtime configurable? I would have expected this type of setting > to be part of the devicetree, which already describes other > parts that interact with sram devices. Register addresses are made runtime configurable to give the user the option of going for a software trigger. So the user can debug issues during run-time as well. These register locations are arbitrary and is configured by the user for debugging purposes and is not related to the DCC hardware itself. > > How does a user ensure that the address they configure does > not overlap with some other use of the sram? The dcc_sram is a dedicated io-memory for exclusive usage by dcc. The register addresses are programmed in the dcc_sram corresponding to a particular list and the start and end location on dcc_sram for a particular list is updated in dcc hardware registers. So no two lists can overlap. This is ensured by the driver code as follows:- /* 3. Program DCC_RAM_CFG reg */ dcc_list_writel(drvdata, ram_cfg_base + drvdata->ram_offset / 4, curr_list, DCC_LL_BASE); dcc_list_writel(drvdata, drvdata->ram_start + drvdata->ram_offset / 4, curr_list, DCC_FD_BASE); > > Arnd