[PATCH v8 1/2] sDMA: descriptor autoloading feature

[Shilimkar, Santosh]

> -----Original Message-----
> From: svenkatr at gmail.com [mailto:svenkatr at gmail.com] On Behalf Of Venkatraman S
> Sent: Wednesday, May 05, 2010 9:56 PM
> To: Shilimkar, Santosh
> Cc: linux-omap at vger.kernel.org; linux-mmc at vger.kernel.org; linux-arm-kernel at lists.infradead.org;
> Chikkature Rajashekar, Madhusudhan; Adrian Hunter; Tony Lindgren
> Subject: Re: [PATCH v8 1/2] sDMA: descriptor autoloading feature
> 
> On Wed, May 5, 2010 at 5:31 PM, Shilimkar, Santosh
> <santosh.shilimkar at ti.com> wrote:
> >
> >
> >> -----Original Message-----
> >> From: svenkatr at gmail.com [mailto:svenkatr at gmail.com] On Behalf Of Venkatraman S
> >> Sent: Wednesday, May 05, 2010 5:20 PM
> >> To: Shilimkar, Santosh
> >> Cc: linux-omap at vger.kernel.org; linux-mmc at vger.kernel.org; linux-arm-kernel at lists.infradead.org;
> >> Chikkature Rajashekar, Madhusudhan; Adrian Hunter; Tony Lindgren
> >> Subject: Re: [PATCH v8 1/2] sDMA: descriptor autoloading feature
> >>
> >> [Long sections have been trimmed to the context of the discussion]
> >> On Wed, May 5, 2010 at 3:02 PM, Shilimkar, Santosh
> >> <santosh.shilimkar at ti.com> wrote:
> >> >> -----Original Message-----
> >> >> +static int dma_sglist_set_phy_params(struct omap_dma_sglist_node *sghead,
> >> >> +             dma_addr_t phyaddr, int nelem)
> >> >> +{
> >> >> +     struct omap_dma_sglist_node *sgcurr, *sgprev;
> >> >> +     dma_addr_t elem_paddr = phyaddr;
> >> >> +
> >> >> +     for (sgprev = sghead;
> >> >> +             sgprev < sghead + nelem;
> >> >> +             sgprev++) {
> >> >> +
> >> >> +             sgcurr = sgprev + 1;
> >> >> +             sgprev->next = sgcurr;
> >> >> +             elem_paddr += (int)sizeof(*sgcurr);
> >> >> +             sgprev->next_desc_add_ptr = elem_paddr;
> >> >> +
> >> >> +             switch (sgcurr->desc_type) {
> >> >> +             case OMAP_DMA_SGLIST_DESCRIPTOR_TYPE1:
> >> >> +                     omap_dma_list_set_ntype(sgprev, 1);
> >> >> +                     break;
> >> >> +
> >> >> +             case OMAP_DMA_SGLIST_DESCRIPTOR_TYPE2a:
> >> >> +             /* intentional no break */
> >> >> +             case OMAP_DMA_SGLIST_DESCRIPTOR_TYPE2b:
> >> >> +                     omap_dma_list_set_ntype(sgprev, 2);
> >> >> +                     break;
> >> >> +
> >> >> +             case OMAP_DMA_SGLIST_DESCRIPTOR_TYPE3a:
> >> >> +                     /* intentional no break */
> >> >> +             case OMAP_DMA_SGLIST_DESCRIPTOR_TYPE3b:
> >> >> +                     omap_dma_list_set_ntype(sgprev, 3);
> >> >> +                     break;
> >> >> +
> >> >> +             default:
> >> >> +                     return -EINVAL;
> >> >> +
> >> >> +             }
> >> > Are we supporting all the descriptor types. I think only type2a is
> >> > supported. In that case please add FIXME, or WARN message here.
> >>
> >> From DMA perspective, all are supported - no restrictions. Only I have
> >> not figured
> >> out how to use type 2b and type 3b descriptors. It's not the fault of
> >> DMA driver or
> >> specification :-) It's actually upto the client to select the right type.
> > OK. Then the question which I wanted to ask.
> > For TX, 2b should have been better choice than 2a isn't it?
> 
> Not much of a difference (as the space allocation is common), but I
> couldn't get 2b working correctly.
> Will try that once I get some clarification from hardware team.
Add a FIXME then with description in the code so that it's not forgotten once the code
is merged.
> 
> >>
> >> >> +
> >> >> +     lcfg->sghead = sgparams;
> >> >> +     lcfg->num_elem = nelem;
> >> >> +     lcfg->sgheadphy = padd;
> >> >> +     lcfg->pausenode = -1;
> >> >> +
> >> >> +
> >> >> +     if (NULL == chparams)
> >> > Minute point really. Better readability "ch_params"
> >> OK