linux-kernel - [PATCH v2 3/7] dma-mapping: introduce the DMA_ATTR_MAY

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Date:   Wed, 19 Apr 2023 12:03:55 +0200
From:   Petr Tesarik <petrtesarik@...weicloud.com>
To:     Jonathan Corbet <corbet@....net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Borislav Petkov <bp@...e.de>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Zhen Lei <thunder.leizhen@...wei.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
        Kim Phillips <kim.phillips@....com>,
        "Steven Rostedt (Google)" <rostedt@...dmis.org>,
        Muchun Song <muchun.song@...ux.dev>,
        Ondrej Zary <linux@...y.sk>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Petr Tesarik <petr.tesarik.ext@...wei.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Won Chung <wonchung@...gle.com>,
        linux-doc@...r.kernel.org (open list:DOCUMENTATION),
        linux-kernel@...r.kernel.org (open list),
        dri-devel@...ts.freedesktop.org (open list:DRM DRIVERS),
        iommu@...ts.linux.dev (open list:DMA MAPPING HELPERS)
Cc:     Roberto Sassu <roberto.sassu@...wei.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>, petr@...arici.cz
Subject: [PATCH v2 3/7] dma-mapping: introduce the DMA_ATTR_MAY_SLEEP attribute

From: Petr Tesarik <petr.tesarik.ext@...wei.com>

Introduce a DMA attribute to tell the DMA-mapping subsystem that
the operation is allowed to sleep.

This patch merely adds the flag, but it does not do anything at
the moment.

Signed-off-by: Petr Tesarik <petr.tesarik.ext@...wei.com>
---
 Documentation/core-api/dma-attributes.rst | 10 ++++++++++
 include/linux/dma-mapping.h               |  6 ++++++
 2 files changed, 16 insertions(+)

diff --git a/Documentation/core-api/dma-attributes.rst b/Documentation/core-api/dma-attributes.rst
index 1887d92e8e92..9ce00926455f 100644
--- a/Documentation/core-api/dma-attributes.rst
+++ b/Documentation/core-api/dma-attributes.rst
@@ -130,3 +130,13 @@ accesses to DMA buffers in both privileged "supervisor" and unprivileged
 subsystem that the buffer is fully accessible at the elevated privilege
 level (and ideally inaccessible or at least read-only at the
 lesser-privileged levels).
+
+DMA_ATTR_MAY_SLEEP
+------------------
+
+This tells the DMA-mapping subsystem that it is allowed to sleep. For example,
+if mapping needs a bounce buffer, software IO TLB may use CMA for the
+allocation if this flag is given.
+
+This attribute is not used for dma_alloc\* functions. Instead, the provided
+GFP flags are used to determine whether the allocation may sleep.
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index 0ee20b764000..7a75c503ac38 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -61,6 +61,12 @@
  */
 #define DMA_ATTR_PRIVILEGED		(1UL << 9)
 
+/*
+ * DMA_ATTR_MAY_SLEEP: This tells the DMA-mapping subsystem that it is allowed
+ * to sleep.
+ */
+#define DMA_ATTR_MAY_SLEEP		(1UL << 10)
+
 /*
  * A dma_addr_t can hold any valid DMA or bus address for the platform.  It can
  * be given to a device to use as a DMA source or target.  It is specific to a
-- 
2.25.1