From: Wolfram Sang <wsa@the-dreams.de> To: Lee Jones <lee.jones@linaro.org> Cc: Bjorn Andersson <bjorn.andersson@linaro.org>, alokc@codeaurora.org, agross@kernel.org, robh+dt@kernel.org, mark.rutland@arm.com, linux-i2c@vger.kernel.org, linux-arm-msm@vger.kernel.org, devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] i2c: qcom-geni: Provide an option to select FIFO processing Date: Thu, 5 Sep 2019 11:16:17 +0200 [thread overview] Message-ID: <20190905091617.GC1157@kunai> (raw) In-Reply-To: <20190905071103.GX26880@dell> [-- Attachment #1: Type: text/plain, Size: 1963 bytes --] Hi Lee, > > It looks like a workaround to me. It would be interesting to hear which > > I2C client breaks with DMA and if it's driver can't be fixed somehow > > instead. But even if we agree on a workaround short term, adding a So, are there investigations running why this reboot happens? > > Is there no other way to disable DMA which is local to this driver so we > > can easily revert the workaround later? > > This is the most local low-impact solution (nomenclature aside). I disagree. You could use of_machine_is_compatible() and disable DMA for that machine. Less impact because we save the workaround binding. > The beautiful thing about this approach is that, *if* the Geni SE DMA I'd say 'advantage' instead of 'beautiful' ;) > ever starts working, we can remove the C code and any old properties > left in older DTs just become NOOP. Older kernels with newer DTs > (less of a priority) *still* won't work, but they don't work now > anyway. Which is a clear disadvantage of that solution. It won't fix older kernels. My suggestion above should fix them, too. > The offending line can be found at [0]. There is no obvious bug to > fix and this code obviously works well on some of the hardware > platforms using it. But on our platform (Lenovo Yoga C630 - QCom > SMD850) that final command, which initiates the DMA transaction, ends > up rebooting the machine. Unless we know why the reboot happens on your platform, I'd be careful with saying "work obviously well" on other platforms. > With regards to the nomenclature, my original suggestion was > 'qcom,geni-se-no-dma'. Would that better suit your request? My suggestion: For 5.3, use of_machine_is_compatible() and we backport that. For later, try to find out the root cause and fix it. If that can't be done, try to set up a generic "disable-dma" property and use it. What do you think about that? Kind regards, Wolfram [-- Attachment #2: signature.asc --] [-- Type: application/pgp-signature, Size: 833 bytes --]
WARNING: multiple messages have this Message-ID (diff)
From: Wolfram Sang <wsa@the-dreams.de> To: Lee Jones <lee.jones@linaro.org> Cc: mark.rutland@arm.com, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org, agross@kernel.org, robh+dt@kernel.org, Bjorn Andersson <bjorn.andersson@linaro.org>, alokc@codeaurora.org, linux-i2c@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH 1/2] i2c: qcom-geni: Provide an option to select FIFO processing Date: Thu, 5 Sep 2019 11:16:17 +0200 [thread overview] Message-ID: <20190905091617.GC1157@kunai> (raw) In-Reply-To: <20190905071103.GX26880@dell> [-- Attachment #1.1: Type: text/plain, Size: 1963 bytes --] Hi Lee, > > It looks like a workaround to me. It would be interesting to hear which > > I2C client breaks with DMA and if it's driver can't be fixed somehow > > instead. But even if we agree on a workaround short term, adding a So, are there investigations running why this reboot happens? > > Is there no other way to disable DMA which is local to this driver so we > > can easily revert the workaround later? > > This is the most local low-impact solution (nomenclature aside). I disagree. You could use of_machine_is_compatible() and disable DMA for that machine. Less impact because we save the workaround binding. > The beautiful thing about this approach is that, *if* the Geni SE DMA I'd say 'advantage' instead of 'beautiful' ;) > ever starts working, we can remove the C code and any old properties > left in older DTs just become NOOP. Older kernels with newer DTs > (less of a priority) *still* won't work, but they don't work now > anyway. Which is a clear disadvantage of that solution. It won't fix older kernels. My suggestion above should fix them, too. > The offending line can be found at [0]. There is no obvious bug to > fix and this code obviously works well on some of the hardware > platforms using it. But on our platform (Lenovo Yoga C630 - QCom > SMD850) that final command, which initiates the DMA transaction, ends > up rebooting the machine. Unless we know why the reboot happens on your platform, I'd be careful with saying "work obviously well" on other platforms. > With regards to the nomenclature, my original suggestion was > 'qcom,geni-se-no-dma'. Would that better suit your request? My suggestion: For 5.3, use of_machine_is_compatible() and we backport that. For later, try to find out the root cause and fix it. If that can't be done, try to set up a generic "disable-dma" property and use it. What do you think about that? Kind regards, Wolfram [-- Attachment #1.2: signature.asc --] [-- Type: application/pgp-signature, Size: 833 bytes --] [-- Attachment #2: Type: text/plain, Size: 176 bytes --] _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2019-09-05 9:16 UTC|newest] Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-09-04 11:36 [PATCH 1/2] i2c: qcom-geni: Provide an option to select FIFO processing Lee Jones 2019-09-04 11:36 ` Lee Jones 2019-09-04 11:36 ` [PATCH 2/2] dt-bindings: soc: qcom: Provide option to select FIFO mode Lee Jones 2019-09-04 11:36 ` Lee Jones 2019-09-04 11:58 ` Vinod Koul 2019-09-04 11:58 ` Vinod Koul 2019-09-04 11:56 ` [PATCH 1/2] i2c: qcom-geni: Provide an option to select FIFO processing Vinod Koul 2019-09-04 11:56 ` Vinod Koul 2019-09-04 12:18 ` Lee Jones 2019-09-04 12:18 ` Lee Jones 2019-09-04 11:58 ` Vinod Koul 2019-09-04 11:58 ` Vinod Koul 2019-09-04 20:35 ` Bjorn Andersson 2019-09-04 20:35 ` Bjorn Andersson 2019-09-04 21:23 ` Wolfram Sang 2019-09-04 21:23 ` Wolfram Sang 2019-09-05 7:11 ` Lee Jones 2019-09-05 7:11 ` Lee Jones 2019-09-05 9:16 ` Wolfram Sang [this message] 2019-09-05 9:16 ` Wolfram Sang 2019-09-05 9:34 ` Lee Jones 2019-09-05 9:34 ` Lee Jones 2019-09-05 13:37 ` Wolfram Sang 2019-09-05 13:37 ` Wolfram Sang
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