linux-kernel - Re: [PATCH v12 3/7] soc: ti: Add IOMMU-like PVU driver

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Message-ID: <bdb5a5e2-3a7e-4050-bf25-c95dfa05138a@siemens.com>
Date: Tue, 29 Jul 2025 18:11:39 +0200
From: Jan Kiszka <jan.kiszka@...mens.com>
To: Nishanth Menon <nm@...com>, huaqian.li@...mens.com
Cc: lkp@...el.com, baocheng.su@...mens.com, bhelgaas@...gle.com,
 christophe.jaillet@...adoo.fr, conor+dt@...nel.org,
 devicetree@...r.kernel.org, diogo.ivo@...mens.com, helgaas@...nel.org,
 kristo@...nel.org, krzk+dt@...nel.org, kw@...ux.com,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-pci@...r.kernel.org, lpieralisi@...nel.org,
 oe-kbuild-all@...ts.linux.dev, robh@...nel.org, s-vadapalli@...com,
 ssantosh@...nel.org, vigneshr@...com
Subject: Re: [PATCH v12 3/7] soc: ti: Add IOMMU-like PVU driver

On 29.07.25 14:22, Nishanth Menon wrote:
> On 10:36-20250728, huaqian.li@...mens.com wrote:
>> From: Jan Kiszka <jan.kiszka@...mens.com>
>>
>> The TI Peripheral Virtualization Unit (PVU) permits to define a limited
>> set of mappings for DMA requests on the system memory. Unlike with an
>> IOMMU, there is no fallback to a memory-backed page table, only a fixed
>> set of register-backed TLBs. Emulating an IOMMU behavior appears to be
>> the more fragile the more fragmentation of pending requests occur.
>>
>> Therefore, this driver does not expose the PVU as an IOMMU. It rather
>> introduces a simple, static interface to devices that are under
>> restricted-dma-pool constraints. They can register their pools with the
>> PVUs, enabling only those pools to work for DMA. As also MSI is issued
>> as DMA, the PVU already register the related translator region of the
>> AM654 as valid DMA target.
>>
>> This driver is the essential building block for limiting DMA from
>> untrusted devices to clearly defined memory regions in the absence of a
>> real IOMMU (SMMU).
>>
>> Co-developed-by: Diogo Ivo <diogo.ivo@...mens.com>
>> Signed-off-by: Diogo Ivo <diogo.ivo@...mens.com>
>> Signed-off-by: Jan Kiszka <jan.kiszka@...mens.com>
>> Signed-off-by: Li Hua Qian <huaqian.li@...mens.com>
>> ---
>>  drivers/soc/ti/Kconfig  |   4 +
>>  drivers/soc/ti/Makefile |   1 +
>>  drivers/soc/ti/ti-pvu.c | 500 ++++++++++++++++++++++++++++++++++++++++
>>  include/linux/ti-pvu.h  |  32 +++
>>  4 files changed, 537 insertions(+)
>>  create mode 100644 drivers/soc/ti/ti-pvu.c
>>  create mode 100644 include/linux/ti-pvu.h
>>
>> diff --git a/drivers/soc/ti/Kconfig b/drivers/soc/ti/Kconfig
>> index 1a93001c9e36..af7173ad84de 100644
>> --- a/drivers/soc/ti/Kconfig
>> +++ b/drivers/soc/ti/Kconfig
>> @@ -82,6 +82,10 @@ config TI_PRUSS
>>  	  processors on various TI SoCs. It's safe to say N here if you're
>>  	  not interested in the PRU or if you are unsure.
>>  
>> +config TI_PVU
>> +	bool "TI Peripheral Virtualization Unit driver"
> 
> tristate please? Prefer to make this as a module.
> 
> 

PCI_KEYSTONE is bool and needs this (if enabled). So this won't be a
module in practice.

Jan

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