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

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Date:   Wed, 25 Mar 2020 16:23:46 +0100
From:   Ludovic BARRE <ludovic.barre@...com>
To:     Ulf Hansson <ulf.hansson@...aro.org>,
        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>,
        Vinod Koul <vkoul@...nel.org>, Haibo Chen <haibo.chen@....com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <dmaengine@...r.kernel.org>, <stable@...r.kernel.org>
Subject: Re: [PATCH 1/2] driver core: platform: Initialize dma_parms for
 platform devices



Le 3/25/20 à 12:34 PM, Ulf Hansson a écrit :
> 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().

tested with mmc: mmci_sdmmc fix
Tested-by: Ludovic Barre <ludovic.barre@...com>

> Suggested-by: Christoph Hellwig <hch@....de>
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
> ---
>   drivers/base/platform.c         | 1 +
>   include/linux/platform_device.h | 1 +
>   2 files changed, 2 insertions(+)
> 
> diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> index b5ce7b085795..46abbfb52655 100644
> --- a/drivers/base/platform.c
> +++ b/drivers/base/platform.c
> @@ -512,6 +512,7 @@ int platform_device_add(struct platform_device *pdev)
>   		pdev->dev.parent = &platform_bus;
>   
>   	pdev->dev.bus = &platform_bus_type;
> +	pdev->dev.dma_parms = &pdev->dma_parms;
>   
>   	switch (pdev->id) {
>   	default:
> 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;
>   
>