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Tue, 17 Oct 2023 08:24:55 GMT Received: from [10.216.24.217] (10.80.80.8) by nalasex01b.na.qualcomm.com (10.47.209.197) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1118.39; Tue, 17 Oct 2023 01:24:47 -0700 Message-ID: Date: Tue, 17 Oct 2023 13:54:43 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 03/11] firmware: qcom-scm: atomically assign and read the global __scm pointer Content-Language: en-US To: Bartosz Golaszewski , Andy Gross , Bjorn Andersson , Konrad Dybcio , Rob Herring , "Krzysztof Kozlowski" , Conor Dooley , Catalin Marinas , Will Deacon , Arnd Bergmann , Alex Elder , Srini Kandagatla CC: , , , , References: <20230828192507.117334-1-bartosz.golaszewski@linaro.org> <20230828192507.117334-4-bartosz.golaszewski@linaro.org> From: Om Prakash Singh In-Reply-To: <20230828192507.117334-4-bartosz.golaszewski@linaro.org> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.80.80.8] X-ClientProxiedBy: nasanex01a.na.qualcomm.com (10.52.223.231) To nalasex01b.na.qualcomm.com (10.47.209.197) X-QCInternal: smtphost X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=5800 signatures=585085 X-Proofpoint-GUID: NZoJXFrXHLjPD7Z3Hv_EfwVC3o2YEwqT X-Proofpoint-ORIG-GUID: NZoJXFrXHLjPD7Z3Hv_EfwVC3o2YEwqT X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.272,Aquarius:18.0.980,Hydra:6.0.619,FMLib:17.11.176.26 definitions=2023-10-16_13,2023-10-12_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxscore=0 suspectscore=0 malwarescore=0 priorityscore=1501 mlxlogscore=999 spamscore=0 bulkscore=0 phishscore=0 impostorscore=0 clxscore=1011 adultscore=0 lowpriorityscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2309180000 definitions=main-2310170069 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/29/2023 12:54 AM, Bartosz Golaszewski wrote: > Checking for the availability of SCM bridge can happen from any context. > It's only by chance that we haven't run into concurrency issues but with > the upcoming SHM Bridge driver that will be initiated at the same > initcall level, we need to assure the assignment and readback of the > __scm pointer is atomic. > > Signed-off-by: Bartosz Golaszewski > --- > drivers/firmware/qcom_scm.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/drivers/firmware/qcom_scm.c b/drivers/firmware/qcom_scm.c > index 980fcfa20b9f..422de70faff8 100644 > --- a/drivers/firmware/qcom_scm.c > +++ b/drivers/firmware/qcom_scm.c > @@ -1331,7 +1331,7 @@ static int qcom_scm_find_dload_address(struct device *dev, u64 *addr) > */ > bool qcom_scm_is_available(void) > { > - return !!__scm; > + return !!READ_ONCE(__scm); > } > EXPORT_SYMBOL(qcom_scm_is_available); > > @@ -1477,8 +1477,8 @@ static int qcom_scm_probe(struct platform_device *pdev) > if (ret) > return ret; > > - __scm = scm; > - __scm->dev = &pdev->dev; > + scm->dev = &pdev->dev; > + WRITE_ONCE(__scm, scm); In my opinion "__scm = scm;" assignment should be done at the end of probe function success so that qcom_scm_is_available() return true only when probe is completed. Other changes may not be needed. > init_completion(&__scm->waitq_comp); >