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

[Venkatraman S]

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 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.
OK. I am assuming the FIXME has to be in MMC driver, not here.