Re: [PATCH] net: macb: Add big endian CPU support

Michal Simek
2015-02-23T14:10:55Z

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Hi Arun,

On 02/20/2015 12:45 PM, Arun Chandran wrote:
> On Thu, Feb 19, 2015 at 5:52 PM, Michal Simek <monstr@monstr.eu> wrote:
>>
>> On 02/18/2015 12:29 PM, Arun Chandran wrote:
>>> This patch converts all __raw_readl and __raw_writel function calls
>>> to their corresponding readl_relaxed and writel_relaxed variants.
>>>
>>> It also tells the driver to set ahb_endian_swp_mgmt_en bit in dma_cfg
>>> when the CPU is configured in big endian mode.
>>>
>>> Signed-off-by: Arun Chandran <achandran@mvista.com>
>>> ---
>>> This patch is tested on xilinx ZC702 evaluation board with
>>> CONFIG_CPU_BIG_ENDIAN=y and booting NFS rootfs
>>> ---
>>> ---
>>> drivers/net/ethernet/cadence/macb.c | 18 ++++++++++++------
>>> drivers/net/ethernet/cadence/macb.h | 15 ++++++++-------
>>> 2 files changed, 20 insertions(+), 13 deletions(-)
>>>
>>> diff --git a/drivers/net/ethernet/cadence/macb.c b/drivers/net/ethernet/cadence/macb.c
>>> index ad76b8e..05fb36d 100644
>>> --- a/drivers/net/ethernet/cadence/macb.c
>>> +++ b/drivers/net/ethernet/cadence/macb.c
>>> @@ -449,7 +449,7 @@ static void macb_update_stats(struct macb *bp)
>>> WARN_ON((unsigned long)(end - p - 1) != (MACB_TPF - MACB_PFR) / 4);
>>>
>>> for(; p < end; p++, reg++)
>>> - *p += __raw_readl(reg);
>>> + *p += readl_relaxed(reg);
>>> }
>>>
>>> static int macb_halt_tx(struct macb *bp)
>>> @@ -1585,7 +1585,11 @@ static void macb_configure_dma(struct macb *bp)
>>> if (bp->dma_burst_length)
>>> dmacfg = GEM_BFINS(FBLDO, bp->dma_burst_length, dmacfg);
>>> dmacfg |= GEM_BIT(TXPBMS) | GEM_BF(RXBMS, -1L);
>>> - dmacfg &= ~GEM_BIT(ENDIA);
>>> + dmacfg &= ~GEM_BIT(ENDIA_PKT);
>>> + /* Tell the chip to byteswap descriptors on big-endian hosts */
>>> +#ifdef __BIG_ENDIAN
>>> + dmacfg |= GEM_BIT(ENDIA_DESC);
>>> +#endif
>>
>> I don't think this is the best way what you should do.
>> Instead of having this ifdef here you should find out any reg and detect if the IP
>> is in big endian or little endian mode. I have done it for some xilinx IPs which
>> can run on big or little endian system.
>> In general find reg which some field which has some meaning - write there 1
>> and read expected value and based on that decide if you are on big or little endian system.
>
> Hi Michal,
>
> I was not able to find any such registers for GEM in the TRM
> http://www.xilinx.com/support/documentation/user_guides/ug585-Zynq-7000-TRM.pdf
>
> I tried writing to dma_cfg (0x00000010) and reading from design_cfg5
> (0x00000290)
> Its not reflecting anything(design_cfg5 always reads same value); It
> is not helping.
>
> The only way (I don't think its not right way either) I can think of
> eliminating that
> #ifdef __BIG_ENDIAN is reading some register in ARM cpu to identify its
> current endianness and write dma_cfg accordingly.

Definitely no to detect cpu endianess.

What about this?
writel(0x2, 0xE000b000); //write little endian
if (readl(0xE000b000) == 0x2) { //read little endian
printf("little endian\n")
disable 0x2 bit (loopback)
} else {
printf("big endian\n");

definitely good to check writing 0x2 here that IP is
in big endian and reacts - if not BUG()
}

I have written this to spi-xilinx.c and you can use similar construction
for macb too (of course with checking above).

/*
* Detect endianess on the IP via loop bit in CR. Detection
* must be done before reset is sent because incorrect reset
* value generates error interrupt.
* Setup little endian helper functions first and try to use them
* and check if bit was correctly setup or not.
*/
xspi->read_fn = xspi_read32;
xspi->write_fn = xspi_write32;

xspi->write_fn(XSPI_CR_LOOP, xspi->regs + XSPI_CR_OFFSET);
tmp = xspi->read_fn(xspi->regs + XSPI_CR_OFFSET);
tmp &= XSPI_CR_LOOP;
if (tmp != XSPI_CR_LOOP) {
xspi->read_fn = xspi_read32_be;
xspi->write_fn = xspi_write32_be;
}

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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