Re: [PATCH 14/18] hw/net: cadence_gem: Add a new 'phy-addr' property

[Bin Meng]

On Sun, Aug 16, 2020 at 8:08 PM Nathan Rossi <nathan@nathanrossi.com> wrote:
>
> On Sun, 16 Aug 2020 at 18:29, Bin Meng <bmeng.cn@gmail.com> wrote:
> >
> > On Sat, Aug 15, 2020 at 5:06 PM Philippe Mathieu-Daudé <f4bug@amsat.org> 
> > wrote:
> > >
> > > On 8/14/20 6:40 PM, Bin Meng wrote:
> > > > From: Bin Meng <bin.meng@windriver.com>
> > > >
> > > > At present the PHY address of the PHY connected to GEM is hard-coded
> > > > to either 23 (BOARD_PHY_ADDRESS) or 0. This might not be the case for
> > > > all boards. Add a new 'phy-addr' property so that board can specify
> > > > the PHY address for each GEM instance.
> > > >
> > > > Signed-off-by: Bin Meng <bin.meng@windriver.com>
> > > > ---
> > > >
> > > >  hw/net/cadence_gem.c         | 7 +++++--
> > > >  include/hw/net/cadence_gem.h | 2 ++
> > > >  2 files changed, 7 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/hw/net/cadence_gem.c b/hw/net/cadence_gem.c
> > > > index a93b5c0..9fa03de 100644
> > > > --- a/hw/net/cadence_gem.c
> > > > +++ b/hw/net/cadence_gem.c
> > > > @@ -1446,7 +1446,8 @@ static uint64_t gem_read(void *opaque, hwaddr 
> > > > offset, unsigned size)
> > > >              uint32_t phy_addr, reg_num;
> > > >
> > > >              phy_addr = (retval & GEM_PHYMNTNC_ADDR) >> 
> > > > GEM_PHYMNTNC_ADDR_SHFT;
> > > > -            if (phy_addr == BOARD_PHY_ADDRESS || phy_addr == 0) {
> > > > +            if (phy_addr == BOARD_PHY_ADDRESS || phy_addr == 0 ||
> > > > +                phy_addr == s->phy_addr) {
> > > >                  reg_num = (retval & GEM_PHYMNTNC_REG) >> 
> > > > GEM_PHYMNTNC_REG_SHIFT;
> > > >                  retval &= 0xFFFF0000;
> > > >                  retval |= gem_phy_read(s, reg_num);
> > > > @@ -1569,7 +1570,8 @@ static void gem_write(void *opaque, hwaddr 
> > > > offset, uint64_t val,
> > > >              uint32_t phy_addr, reg_num;
> > > >
> > > >              phy_addr = (val & GEM_PHYMNTNC_ADDR) >> 
> > > > GEM_PHYMNTNC_ADDR_SHFT;
> > > > -            if (phy_addr == BOARD_PHY_ADDRESS || phy_addr == 0) {
> > > > +            if (phy_addr == BOARD_PHY_ADDRESS || phy_addr == 0 ||
> > > > +                phy_addr == s->phy_addr) {
> > > >                  reg_num = (val & GEM_PHYMNTNC_REG) >> 
> > > > GEM_PHYMNTNC_REG_SHIFT;
> > > >                  gem_phy_write(s, reg_num, val);
> > > >              }
> > > > @@ -1682,6 +1684,7 @@ static Property gem_properties[] = {
> > > >      DEFINE_NIC_PROPERTIES(CadenceGEMState, conf),
> > > >      DEFINE_PROP_UINT32("revision", CadenceGEMState, revision,
> > > >                         GEM_MODID_VALUE),
> > > > +    DEFINE_PROP_UINT8("phy-addr", CadenceGEMState, phy_addr, 0),
> > >
> > > This patch would be complete by moving the BOARD_PHY_ADDRESS definition
> > > to each board using this NIC, and setting the "phy-addr" property to
> > > this value.
> >
> > I actually have no idea which board in QEMU is using this special PHY
> > address instead of default 0.
>
> Given Xilinx's QEMU fork has not used this value for quite some time,
> I suspect it was only used to match an early chip emulation
> platform/board.
>
> https://github.com/Xilinx/qemu/blame/master/hw/net/cadence_gem.c#L248
>
> >
> > It looks BOARD_PHY_ADDRESS has been there since the initial version of
> > the cadence_gem model.
> >
> > commit e9f186e514a70557d695cadd2c2287ef97737023
> > Author: Peter A. G. Crosthwaite <peter.crosthwaite@petalogix.com>
> > Date:   Mon Mar 5 14:39:12 2012 +1000
> >
> >     cadence_gem: initial version of device model
> >
> >     Device model for cadence gem ethernet controller.
> >
> >     Signed-off-by: Peter A. G. Crosthwaite <peter.crosthwaite@petalogix.com>
> >     Signed-off-by: John Linn <john.linn@xilinx.com>
> >     Acked-by: Edgar E. Iglesias <edgar.iglesias@gmail.com>
> >     Signed-off-by: Edgar E. Iglesias <edgar.iglesias@gmail.com>
> >
> > Later PHY address 0 was added via the following commit:
> >
> > commit 553893736885e4f2dda424bff3e2200e1b6482a5
> > Author: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
> > Date:   Thu Apr 3 23:55:19 2014 -0700
> >
> >     net: cadence_gem: Make phy respond to broadcast
> >
> >     Phys must respond to address 0 by specification. Implement.
> >
> >     Signed-off-by: Nathan Rossi <nathan.rossi@xilinx.com>
> >     Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
> >     Message-id:
> > 6f4d53b04ddbfb19895bfb61a595e69f1c08859a.1396594056.git.peter.crosthwaite@xilinx.com
> >     Reviewed-by: Beniamino Galvani <b.galvani@gmail.com>
> >     Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> >
> > I doubt the commit message said that PHYs must respond to address 0. I
> > am not aware of such specs. The issue was probably that whatever board
> > 2nd commit was tested against did not have a PHY at address
> > BOARD_PHY_ADDRESS.
>
> It is common for phy devices to support it as a broadcast address. It
> is also commonly written in Xilinx documentation that it is treated as
> a broadcast address. e.g. the axi ethernet core
> (https://www.xilinx.com/support/documentation/ip_documentation/axi_ethernet/v7_0/pg138-axi-ethernet.pdf
> page 45). But 802.3 does not require it, instead address 0 is only
> reserved.
>
> With this commit the "must" refers to the device specification, in
> that QEMU is emulating a real phy (though more specifically the phy(s)
> that were being emulated for Zynq boards) that does respond to address
> 0 as a broadcast. This change was a trade off in order to make QEMU
> behave as it would on hardware, such that software using address 0 as
> broadcast would work correctly.
>

Thanks Nathan. So is it safe to just remove BOARD_PHY_ADDRESS and set
"phy-addr" property default value to 0?

Regards,
Bin