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SubjectRe: [PATCH v2 2/2] usb: gadget: Add xilinx axi usb2 device support
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Hi Michal,

On Thu, Apr 3, 2014 at 8:53 PM, Michal Simek <monstr@monstr.eu> wrote:
>>> +struct xusb_udc {
>>> + struct usb_gadget gadget;
>>> + struct xusb_ep ep[8];
>>> + struct usb_gadget_driver *driver;
>>> + struct cmdbuf ch9cmd;
>>> + u32 usb_state;
>>> + u32 remote_wkp;
>>> + unsigned int (*read_fn)(void __iomem *);
>>> + void (*write_fn)(void __iomem *, u32, u32);
>>
>> why do you need these to be function pointers ? Because of endianness ?
>> generic readl()/writel() already take care of that.
>
> readl from asm-generic/io.h is converting value from little endian IO
> to cpu endianness.
> This IP exists also in big endian version.
> It means we have to support all possible combinations.
> IP little and reading it on little or big endian CPU
> IP big and reading it on little or big endian CPU.
>
> Look below.
>
>>> + spin_lock_init(&udc->lock);
>>> +
>>> + /* Check for IP endianness */
>>> + udc->write_fn = xudc_write32_be;
>>> + udc->read_fn = xudc_read32_be;
>>> + udc->write_fn(udc->base_address, XUSB_TESTMODE_OFFSET, TEST_J);
>>> + if ((udc->read_fn(udc->base_address + XUSB_TESTMODE_OFFSET))
>>> + != TEST_J) {
>>> + udc->write_fn = xudc_write32;
>>> + udc->read_fn = xudc_read32;
>>> + }
>>
>> hmm... isn't there a configuration register to check this out ?
>
> Sundeep can tell us if there is any configuration register but
> I don't think so in connection to my experience with Xilinx soft IPs.
>

Yes, there is no configuration register for endianess.

Thanks,
Sundeep.

> Endian detection directly on IP itself came from my discussion
> on drivers/spi/spi-xilinx.c that this is only one way how to do it.
>
> Thanks,
> Michal
>
> --
> Michal Simek, Ing. (M.Eng), OpenPGP -> KeyID: FE3D1F91
> w: www.monstr.eu p: +42-0-721842854
> Maintainer of Linux kernel - Microblaze cpu - http://www.monstr.eu/fdt/
> Maintainer of Linux kernel - Xilinx Zynq ARM architecture
> Microblaze U-BOOT custodian and responsible for u-boot arm zynq platform
>
>


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