netdev - Re: [PATCH v4 9/9] net-next: New ax88796 platform driver for Amiga X-Surf 100 Zorro board (m68k)

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Date:   Sat, 9 Jun 2018 11:15:11 +0200
From:   "Michael Karcher" <michael.karcher@...berlin.de>
To:     "Michael Schmitz" <schmitzmic@...il.com>
Cc:     "Geert Uytterhoeven" <geert@...ux-m68k.org>,
        "netdev" <netdev@...r.kernel.org>, "Andrew Lunn" <andrew@...n.ch>,
        "Finn Thain" <fthain@...egraphics.com.au>,
        "Florian Fainelli" <f.fainelli@...il.com>,
        "Linux/m68k" <linux-m68k@...r.kernel.org>,
        "Michael Karcher" <kernel@...rcher.dialup.fu-berlin.de>
Subject: Re: [PATCH v4 9/9] net-next: New ax88796 platform driver for Amiga
 X-Surf 100 Zorro board (m68k)

Michael Schmitz schrieb:
> Hi Michael,
>> actually, the the block_input / block_output functions were the reason I
>> included the lib8390.c file. Except for xs100_write / xs100_read, they
>> are
>> a verbatim copy from ax88796.c I'm not that enthusiastic about that idea
>> anymore, but did not get around to improve it. I added a customization
>> point to ax88796 for a custom block_input / block_output, because the
>> 8390
>> core already provides that customization point. What I really need is a
>> customization point just for the 8390-remote-DMA-via-MMIO functions
>> (i.e.
>> xs100_write, xs100_read) instead of the whole block transfer core that
>> also sets up the remote DMA engine and tries to re-initialize the card
>> in
>> case of unexplained problems.
>
> OK, so essentially change
>
>          if (ei_local->word16) {
>                  ioread16_rep(nic_base + NE_DATAPORT, buf, count >> 1);
>                  if (count & 0x01)
>                          buf[count-1] = ei_inb(nic_base + NE_DATAPORT);
>
>          } else {
>                  ioread8_rep(nic_base + NE_DATAPORT, buf, count);
>          }
>
> to something like
>
>          if (ax->block_read) {
> 		ax->block_read(dev, buf, count);
> 	} else if (ei_local->word16) {
>                  ioread16_rep(nic_base + NE_DATAPORT, buf, count >> 1);
>                  if (count & 0x01)
>                          buf[count-1] = ei_inb(nic_base + NE_DATAPORT);
>
>          } else {
>                  ioread8_rep(nic_base + NE_DATAPORT, buf, count);
>          }
>
> and populate ax->block_read() and ax_block_write() from platform data,
> instead of substituting ax_block_input() / ax_block_output() wholesale?

That's basically how I think the whole lib8390.c story should in fact be
tackled. Less code duplication, no second include of lib8390 and constrain
xsurf100.c to the pieces that make this piece of hardware unique.

> I must be missing something here.

I don't think so.

> Adds one test for
> ax->block_read on the critical path but we already have the test for
> ei_local->word16 there. May need rearranging the tests so the majority
> of ax88796 users isn't impacted.
Rearranging sounds like a good idea. As I understand, the only valid
rearrangement is putting it inside the 16-bit branch, because the xs100
uses 16-bit transfers and needs the extra byte for odd counts. The code
checks word16 at the beginning of xs100_block_output for that. This has
the advantage of not hurting users of the 8 bit interface, which might be
the slowest users of the ax88796, but comes at the cost of not being able
to customize the block_input/block_output for 8-bit users. As this "cost"
is not a problem now (no one can customize block_input/block_output
currently), lets put the block_read check into the word16 block. You might
want to name the member block_read16 instead of just block_read to convey
the information, that it is only used if word16 is set.

> Anyway, your code, your call.
On the other hand: Your polishing, your call. Thank you for your work on
gettting the code in good shape for merging.

Kind regards,
  Michael Karcher