linux-kernel - Re: [PATCH 2/2] amba: Initialize dma

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Date:   Wed, 25 Mar 2020 16:24:03 +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 2/2] amba: Initialize dma_parms for amba devices



Le 3/25/20 à 12:34 PM, Ulf Hansson a écrit :
> It's currently the amba 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 amba 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: Russell King <linux@...linux.org.uk>
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
> ---
>   drivers/amba/bus.c       | 2 ++
>   include/linux/amba/bus.h | 1 +
>   2 files changed, 3 insertions(+)
> 
> diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c
> index fe1523664816..5e61783ce92d 100644
> --- a/drivers/amba/bus.c
> +++ b/drivers/amba/bus.c
> @@ -374,6 +374,8 @@ static int amba_device_try_add(struct amba_device *dev, struct resource *parent)
>   	WARN_ON(dev->irq[0] == (unsigned int)-1);
>   	WARN_ON(dev->irq[1] == (unsigned int)-1);
>   
> +	dev->dev.dma_parms = &dev->dma_parms;
> +
>   	ret = request_resource(parent, &dev->res);
>   	if (ret)
>   		goto err_out;
> diff --git a/include/linux/amba/bus.h b/include/linux/amba/bus.h
> index 26f0ecf401ea..0bbfd647f5c6 100644
> --- a/include/linux/amba/bus.h
> +++ b/include/linux/amba/bus.h
> @@ -65,6 +65,7 @@ struct amba_device {
>   	struct device		dev;
>   	struct resource		res;
>   	struct clk		*pclk;
> +	struct device_dma_parameters dma_parms;
>   	unsigned int		periphid;
>   	unsigned int		cid;
>   	struct amba_cs_uci_id	uci;
>