zorro_esp, was Re: m68k v3.16 status update

[Finn Thain <fthain@telegraphics.com.au>]

On Tue, 19 Dec 2017, Michael Schmitz wrote:

> > 
> > > Contrary to the Mac driver, esp->command_block and 
> > > esp->command_block_dma are not identical addresses on Amiga.
> > 
> > Why not make them identical, depending on the length of the tranfer? 
> > (Then choose PIO or DMA by testing for the same threshold.)
> 
> esp->command_block_dma is mapped at driver init time so we don't get to 
> chose at command submission time.

You could set esp->command_block_dma to an address like 0xffffffff. Then 
when zorro_esp's ops->send_dma_cmd method is to do a DMA to or from that 
address, check the transfer length. If the length is small, use 
esp->command_block as the address for a PIO transfer. Otherwise, use the 
mapped esp->command_block (which you saved somewhere at driver init time) 
for a DMA transfer.

This is a hack, of course. Perhaps we can avoid the hack if we pass the 
virtual address as an argument to ops->send_dma_cmd.

(Or *sg could be passed, if we cook up a couple of scattergather structs 
to replace ent->sense_ptr and esp->command_block. This might allow for the 
elimination of ops->map_single and ops->unmap_single altogether...)

> > 
> > > (I can use esp->command_block in the reconnect message special case 
> > > but not otherwise ...)
> > 
> > Maybe something like this...
> > 
> > 	struct esp_cmd_entry *ent = esp->active_cmd;
> > 	struct esp_cmd_priv *spriv = ESP_CMD_PRIV(ent->cmd);
> > 	struct scatterlist *sg = spriv->cur_sg;
> > 	unsigned long addr = sg_page(sg) + sg->offset;
> > 
> > but that doesn't work for the esp_autosense() case, which doesn't 
> > involve esp->ops->map_sg...
> > 
> > HTH
> 
> I'll give that a try to see if this works for regular transfers.
> 
> Will look at ways to identify autosense as well (do sense data fit into 
> the ESP FIFO usually?)

You can identify the autosense case easily enough,

	struct esp_cmd_entry *ent = esp->active_cmd;
	struct esp_cmd_priv *spriv = ESP_CMD_PRIV(ent->cmd);
	unsigned long addr;

	if (ent->flags & ESP_CMD_FLAG_AUTOSENSE)
		addr = spriv->sense_ptr;
	else {
		struct scatterlist *sg = spriv->cur_sg;

		addr = sg_page(sg) + sg->offset;
	}

But that still leaves the command_block case unhandled (I don't think we 
can use spriv->cur_sg for that, so we'd need a hack like the one above). 

All this complexity doesn't really belong in the ops->send_dma_cmd method, 
so I think we are back to passing in the virtual pointer as a parameter. 

That change would touch every esp driver. But it could improve mac_esp, 
since mac_esp would no longer have to do any fake dma mapping. Maybe I 
should do a patch for this?

-- 

> 
> Cheers,
> 
> 	Michael
> 
>