[U-Boot] [PATCH] net: designware: set the PS bit when resetting DMA bus in MII configuration

[Joe Hershberger]

On Mon, Jun 4, 2018 at 5:17 AM, Quentin Schulz
<quentin.schulz at bootlin.com> wrote:
> On the SPEAr600 SoC, which has the dwmac1000 variant of the IP block,
> the DMA reset never succeeds when a MII PHY is used (no problem with a
> GMII PHY). The designware_eth_init() function sets the
> DMAMAC_SRST bit in the DMA_BUS_MODE register, and then
> polls until this bit clears. When a MII PHY is used, with the current
> driver, this bit never clears and the driver therefore doesn't work.
>
> The reason is that the PS bit of the GMAC_CONTROL register should be
> correctly configured for the DMA reset to work. When the PS bit is 0,
> it tells the MAC we have a GMII PHY, when the PS bit is 1, it tells
> the MAC we have a MII PHY.
>
> Doing a DMA reset clears all registers, so the PS bit is cleared as
> well. This makes the DMA reset work fine with a GMII PHY. However,
> with MII PHY, the PS bit should be set.
>
> We have identified this issue thanks to two SPEAr600 platform:
>
> - One equipped with a GMII PHY, with which the existing driver was
> working fine.
>
> - One equipped with a MII PHY, where the current driver fails because
> the DMA reset times out.
>
> Note: Taken from https://www.spinics.net/lists/netdev/msg432578.html
>
> Signed-off-by: Quentin Schulz <quentin.schulz at bootlin.com>
> ---
>
> Note, it looks like dw_adjust_link[1] already tries to handle this.
> However, the condition is the speed of the link (if not 1Gbps set
> the bit), not the mode of communication between the MAC and the PHY.
> We could definitely have a 100Mbps with e.g. a GMII mode, and thus we
> should not clear the MII_PORTSELECT bit.
>
> Do you agree with regards to the commit log above?

Yeah, that seems right.

> [1] https://elixir.bootlin.com/u-boot/latest/source/drivers/net/designware.c#L243
>
>  drivers/net/designware.c |  9 +++++++++
>  1 file changed, 9 insertions(+)
>

Acked-by: Joe Hershberger <joe.hershberger at ni.com>