linux-kernel - Re: [PATCH v2 2/2] usb: ehci: Add Aspeed AST2700 support

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Message-ID: <69e6fd9c-6020-4caf-b6e4-644ae794d421@rowland.harvard.edu>
Date: Fri, 26 Sep 2025 11:15:36 -0400
From: Alan Stern <stern@...land.harvard.edu>
To: Ryan Chen <ryan_chen@...eedtech.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, linux-usb@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] usb: ehci: Add Aspeed AST2700 support

On Fri, Sep 26, 2025 at 10:33:08AM +0800, Ryan Chen wrote:
> Unlike earlier Aspeed SoCs (AST2400/2500/2600) which are limited to
> 32-bit DMA addressing, the EHCI controller in AST2700 supports 64-bit
> DMA. Update the EHCI platform driver to make use of this capability by
> selecting a 64-bit DMA mask when the "aspeed,ast2700-ehci" compatible
> is present in device tree.
> 
> Signed-off-by: Ryan Chen <ryan_chen@...eedtech.com>
> ---
>  drivers/usb/host/ehci-platform.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/host/ehci-platform.c b/drivers/usb/host/ehci-platform.c
> index 6aab45c8525c..18e231d345d0 100644
> --- a/drivers/usb/host/ehci-platform.c
> +++ b/drivers/usb/host/ehci-platform.c
> @@ -27,6 +27,7 @@
>  #include <linux/io.h>
>  #include <linux/module.h>
>  #include <linux/of.h>
> +#include <linux/of_device.h>
>  #include <linux/platform_device.h>
>  #include <linux/reset.h>
>  #include <linux/sys_soc.h>
> @@ -239,6 +240,7 @@ static int ehci_platform_probe(struct platform_device *dev)
>  	struct usb_hcd *hcd;
>  	struct resource *res_mem;
>  	struct usb_ehci_pdata *pdata = dev_get_platdata(&dev->dev);
> +	const struct of_device_id *match;
>  	struct ehci_platform_priv *priv;
>  	struct ehci_hcd *ehci;
>  	int err, irq, clk = 0;
> @@ -253,6 +255,10 @@ static int ehci_platform_probe(struct platform_device *dev)
>  	if (!pdata)
>  		pdata = &ehci_platform_defaults;
>  
> +	match = of_match_device(dev->dev.driver->of_match_table, &dev->dev);
> +	if (match && match->data)
> +		pdata->dma_mask_64 = 1;

You must not do this, since pdata may be pointing to the static 
ehci_platform_defaults structure.  Instead, set a local variable to the 
value of pdata->dma_mask_64, and if match->data is set then update the 
local variable.  

> +
>  	err = dma_coerce_mask_and_coherent(&dev->dev,
>  		pdata->dma_mask_64 ? DMA_BIT_MASK(64) : DMA_BIT_MASK(32));

Then use the local variable here to select which DMA mask is used.

Alan Stern