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Tue, 17 Oct 2023 01:30:09 -0700 (PDT) Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20230828192507.117334-1-bartosz.golaszewski@linaro.org> <20230828192507.117334-4-bartosz.golaszewski@linaro.org> In-Reply-To: From: Bartosz Golaszewski Date: Tue, 17 Oct 2023 10:29:58 +0200 Message-ID: Subject: Re: [PATCH 03/11] firmware: qcom-scm: atomically assign and read the global __scm pointer To: Om Prakash Singh Cc: Andy Gross , Bjorn Andersson , Konrad Dybcio , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Catalin Marinas , Will Deacon , Arnd Bergmann , Alex Elder , Srini Kandagatla , kernel@quicinc.com, linux-arm-msm@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net On Tue, 17 Oct 2023 at 10:25, Om Prakash Singh wrote: > > > > 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. > Om, this is v1. We're at v4 (soon v5). I agree with the comment but it's outside the scope of this series. I may address it later. It has been like this for a long time. Typically this module is built-in and initialized before all other drivers so it has never caused problems. Bart > > init_completion(&__scm->waitq_comp); > >