linux-kernel - [PATCH v2 1/2] driver core: platform: Initialize dma

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Date:   Tue, 31 Mar 2020 20:38:43 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        linux-kernel@...r.kernel.org
Cc:     Arnd Bergmann <arnd@...db.de>, Christoph Hellwig <hch@....de>,
        Russell King <linux@...linux.org.uk>,
        Linus Walleij <linus.walleij@...aro.org>,
        Robin Murphy <robin.murphy@....com>,
        Vinod Koul <vkoul@...nel.org>, Haibo Chen <haibo.chen@....com>,
        Ludovic Barre <ludovic.barre@...com>,
        linux-arm-kernel@...ts.infradead.org, dmaengine@...r.kernel.org,
        Ulf Hansson <ulf.hansson@...aro.org>, stable@...r.kernel.org
Subject: [PATCH v2 1/2] driver core: platform: Initialize dma_parms for platform devices

It's currently the platform driver's responsibility to initialize the
pointer, dma_parms, for its corresponding struct device. The benefit with
this approach allows us to avoid the initialization and to not waste memory
for the struct device_dma_parameters, as this can be decided on a case by
case basis.

However, it has turned out that this approach is not very practical.  Not
only does it lead to open coding, but also to real errors. In principle
callers of dma_set_max_seg_size() doesn't check the error code, but just
assumes it succeeds.

For these reasons, let's do the initialization from the common platform bus
at the device registration point. This also follows the way the PCI devices
are being managed, see pci_device_add().

Suggested-by: Christoph Hellwig <hch@....de>
Cc: <stable@...r.kernel.org>
Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>

---

Changes in v2:
	- Move initialization to setup_pdev_dma_masks(). This means the
	initialization is done also in the OF path.

---
 drivers/base/platform.c         | 2 ++
 include/linux/platform_device.h | 1 +
 2 files changed, 3 insertions(+)

diff --git a/drivers/base/platform.c b/drivers/base/platform.c
index b5ce7b085795..c81b68d5d66d 100644
--- a/drivers/base/platform.c
+++ b/drivers/base/platform.c
@@ -361,6 +361,8 @@ struct platform_object {
  */
 static void setup_pdev_dma_masks(struct platform_device *pdev)
 {
+	pdev->dev.dma_parms = &pdev->dma_parms;
+
 	if (!pdev->dev.coherent_dma_mask)
 		pdev->dev.coherent_dma_mask = DMA_BIT_MASK(32);
 	if (!pdev->dev.dma_mask) {
diff --git a/include/linux/platform_device.h b/include/linux/platform_device.h
index 041bfa412aa0..81900b3cbe37 100644
--- a/include/linux/platform_device.h
+++ b/include/linux/platform_device.h
@@ -25,6 +25,7 @@ struct platform_device {
 	bool		id_auto;
 	struct device	dev;
 	u64		platform_dma_mask;
+	struct device_dma_parameters dma_parms;
 	u32		num_resources;
 	struct resource	*resource;
 
-- 
2.20.1