Messages in this thread | | | From | "" <> | Subject | RE: [PATCH] iommu/arm-smmu-v3: fixed check process for disable_bypass module parameter | Date | Wed, 3 Aug 2022 12:45:09 +0000 |
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Hi, Robin, Thank you for your comments.
> > /* Enable the SMMU interface, or ensure bypass */ > > - if (!bypass || disable_bypass) { > > + if (!bypass && disable_bypass) { > > This change looks obviously wrong - if bypass is false here then we definitely > want to enable the SMMU, so disable_bypass is irrelevant. It shouldn't even be > possible to get here with bypass==true under ACPI, since > arm_smmu_device_acpi_probe() cannot fail :/
Sorry, my understanding of the meaning of the disable_bypass module parameter and the process of setting GBPA_ABORT was insufficient.
I misunderstood that the disable_bypass module parameter is used to simply bypass (disable) SMMU (SMMU_CR0.SMMUEN == 0 and SMMU_GBPA.ABORT == 0). Forget about the fixes in this patch.
Although our understanding was lacking, we thought it would be a good idea to have a module parameter that simply disables SMMU, so we were considering a fix.
Best regards, Shuuichirou.
> -----Original Message----- > From: Robin Murphy <robin.murphy@arm.com> > Sent: Wednesday, August 3, 2022 6:26 PM > To: Ishii, Shuuichirou/石井 周一郎 <ishii.shuuichir@fujitsu.com>; > will@kernel.org; joro@8bytes.org; thunder.leizhen@huawei.com; jgg@ziepe.ca; > tglx@linutronix.de; chenxiang66@hisilicon.com; christophe.jaillet@wanadoo.fr; > john.garry@huawei.com; baolu.lu@linux.intel.com; > linux-arm-kernel@lists.infradead.org; iommu@lists.linux.dev; > linux-kernel@vger.kernel.org > Subject: Re: [PATCH] iommu/arm-smmu-v3: fixed check process for > disable_bypass module parameter > > On 2022-08-03 00:42, Shuuichirou Ishii wrote: > > The current process does not enable the bypass setting regardless of > > the value of the disable_bypass module parameter when ACPI is enabled, > > so the value of the disable_bypass module parameter has been corrected > > so that it is handled correctly. > > > > Signed-off-by: Shuuichirou Ishii <ishii.shuuichir@fujitsu.com> > > --- > > drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c > > b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c > > index 88817a3376ef..256d7b2a83a7 100644 > > --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c > > +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c > > @@ -3396,7 +3396,7 @@ static int arm_smmu_device_reset(struct > arm_smmu_device *smmu, bool bypass) > > enables &= ~(CR0_EVTQEN | CR0_PRIQEN); > > > > /* Enable the SMMU interface, or ensure bypass */ > > - if (!bypass || disable_bypass) { > > + if (!bypass && disable_bypass) { > > This change looks obviously wrong - if bypass is false here then we definitely > want to enable the SMMU, so disable_bypass is irrelevant. It shouldn't even be > possible to get here with bypass==true under ACPI, since > arm_smmu_device_acpi_probe() cannot fail :/ > Robin. > > > enables |= CR0_SMMUEN; > > } else { > > ret = arm_smmu_update_gbpa(smmu, 0, GBPA_ABORT);
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