Re: [PATCH] ftgmac100: Implement variable descriptor size

[Erik Smit]

On Wed, 3 Jun 2020 at 10:16, Cédric Le Goater <clg@kaod.org> wrote:
>
> On 6/2/20 6:47 PM, Erik Smit wrote:
> > The hardware supports variable descriptor sizes, configured with the DBLAC
> > register.
>
> yes.
>
> The DBLAC default value is 0x00022F00 on AST2400 and 0x00022500 on AST2500
> and AST2600. The current reset handler needs a little fix btw.
>
> This sets the TX and RX descriptor default size to 4 words (2 * 8bytes).
>
> > Most drivers use the default 2*8, which is currently hardcoded in qemu, but
> > the implementation of the driver in Supermicro BMC SMT_X11_158 uses 4*8.
>
> The first 4 words are architected but the specs allows the descriptors
> to be bigger which is what the Aspeed SDK is doing:
>
>         outl( 0x44f97, dev->base_addr + DBLAC_REG );
>
> It's using 8 words ( 4 * 8bytes) to store some address in the fifth.
> This is a waste btw.
>
>
> Thanks for spotting this. I think the patch is correct but we need to
> clarify a few things.
>
> > --
> > The implementation of the driver in Supermicro BMC SMT_X11_158 adds 4 extra
> > 4-bytes entries:
> > https://github.com/ya-mouse/openwrt-linux-aspeed/blob/master/drivers/net/ftgmac100_26.h#L387-L391
> >
> > And sets DBLAC to 0x44f97:
> > https://github.com/ya-mouse/openwrt-linux-aspeed/blob/master/drivers/net/ftgmac100_26.c#L449
> >
> > There's not a lot of public documentation on this hardware, but the
> > current linux driver shows the meaning of these registers:
> >
> > https://github.com/torvalds/linux/blob/master/drivers/net/ethernet/faraday/ftgmac100.c#L280-L281
> >
> >         iowrite32(FTGMAC100_DBLAC_RXDES_SIZE(2) |   /* 2*8 bytes RX descs */
> >                   FTGMAC100_DBLAC_TXDES_SIZE(2) |   /* 2*8 bytes TX descs */
> >
> > Without this patch, networking in SMT_X11_158 does not pass data.
> >
> > Signed-off-by: Erik Smit <erik.lucas.smit@gmail.com 
> > <mailto:erik.lucas.smit@gmail.com>>
> > ---
> >  hw/net/ftgmac100.c | 17 +++++++++++++++--
> >  1 file changed, 15 insertions(+), 2 deletions(-)
> >
> > diff --git a/hw/net/ftgmac100.c b/hw/net/ftgmac100.c
> > index 25ebee7ec2..1640b24b23 100644
> > --- a/hw/net/ftgmac100.c
> > +++ b/hw/net/ftgmac100.c
> > @@ -79,6 +79,19 @@
> >  #define FTGMAC100_APTC_TXPOLL_CNT(x)        (((x) >> 8) & 0xf)
> >  #define FTGMAC100_APTC_TXPOLL_TIME_SEL      (1 << 12)
> >
> > +/*
> > + * DMA burst length and arbitration control register
> > + */
> > +#define FTGMAC100_DBLAC_RXFIFO_LTHR(x)      (((x) >> 0) & 0x7)
> > +#define FTGMAC100_DBLAC_RXFIFO_HTHR(x)      (((x) >> 3) & 0x7)
> > +#define FTGMAC100_DBLAC_RX_THR_EN           (1 << 6)
>
> The above definitions are AST2400 only. We should say so or leave them out
> because the model does not use them any how.

Like so?

#define FTGMAC100_DBLAC_RXFIFO_LTHR(x)      (((x) >> 0) & 0x7)  // AST2400-only
#define FTGMAC100_DBLAC_RXFIFO_HTHR(x)      (((x) >> 3) & 0x7)  // AST2400-only
#define FTGMAC100_DBLAC_RX_THR_EN           (1 << 6)            // AST2400-only

>
> > +#define FTGMAC100_DBLAC_RXBURST_SIZE(x)     (((x) >> 8) & 0x3)
> > +#define FTGMAC100_DBLAC_TXBURST_SIZE(x)     (((x) >> 10) & 0x3)
> > +#define FTGMAC100_DBLAC_RXDES_SIZE(x)       (((x) >> 12) & 0xf)
> > +#define FTGMAC100_DBLAC_TXDES_SIZE(x)       (((x) >> 16) & 0xf)
>
> I would include '* 8' in the {R,T}XDES_SIZE macros

Agreed.

> > +#define FTGMAC100_DBLAC_IFG_CNT(x)          (((x) >> 20) & 0x7)
> > +#define FTGMAC100_DBLAC_IFG_INC             (1 << 23)
> > +
> >  /*
> >   * PHY control register
> >   */
> > @@ -553,7 +566,7 @@ static void ftgmac100_do_tx(FTGMAC100State *s, uint32_t 
> > tx_ring,
> >          if (bd.des0 & s->txdes0_edotr) {
> >              addr = tx_ring;
> >          } else {
> > -            addr += sizeof(FTGMAC100Desc);
> > +            addr += (FTGMAC100_DBLAC_TXDES_SIZE(s->dblac)) * 8;
>
> and remove the '* 8' here.

Agreed.

> >          }
> >      }
> >
> > @@ -982,7 +995,7 @@ static ssize_t ftgmac100_receive(NetClientState *nc, 
> > const uint8_t *buf,
> >          if (bd.des0 & s->rxdes0_edorr) {
> >              addr = s->rx_ring;
> >          } else {
> > -            addr += sizeof(FTGMAC100Desc);
> > +            addr += (FTGMAC100_DBLAC_RXDES_SIZE(s->dblac)) * 8;
> >          }
> >      }
> >      s->rx_descriptor = addr;
>
>
> and when the DBLAC register is set, we should check the size values to make
> sure they are not under sizeof(FTGMAC100Desc), in which case we should
> report an error.

Like so?

    case FTGMAC100_DBLAC: /* DMA Burst Length and Arbitration Control */
        s->dblac = value;
        if (FTGMAC100_DBLAC_TXDES_SIZE(s->dblac) < sizeof(FTGMAC100Desc))
            qemu_log_mask(LOG_GUEST_ERROR, "%s: transmit descriptor
too small : %d bytes\n",
                              __func__, FTGMAC100_DBLAC_TXDES_SIZE(s->dblac));
        if (FTGMAC100_DBLAC_RXDES_SIZE(s->dblac) < sizeof(FTGMAC100Desc))
            qemu_log_mask(LOG_GUEST_ERROR, "%s: receive descriptor too
small : %d bytes\n",
                              __func__, FTGMAC100_DBLAC_RXDES_SIZE(s->dblac));
        break;

Also, I've not got experience submitting patches to Qemu. My next step
would be to respin this patch and resend it to everybody as [PATCH
v2]?

Best regards,

Erik Smit