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

[Venkatraman S]

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.

>>
>> >> +
>> >> +     lcfg->sghead = sgparams;
>> >> +     lcfg->num_elem = nelem;
>> >> +     lcfg->sgheadphy = padd;
>> >> +     lcfg->pausenode = -1;
>> >> +
>> >> +
>> >> +     if (NULL == chparams)
>> > Minute point really. Better readability "ch_params"
>> OK
>>
>> >> +     dma_write(l, CDP(lch));
>> >> +     dma_write((lcfg->sgheadphy), CNDP(lch));
>> >> +     /**
>> >> +      * Barrier needed as writes to the
>> >> +      * descriptor memory needs to be flushed
>> >> +      * before it's used by DMA controller
>> >> +      */
>> > Little bit of re-wording if you can.
>> > Also you don't wanted the double **
>> >        /*
>> >         * Memory barrier is needed because data may still be
>> >         * in the write buffer. The barrier drains write buffers and
>> >         * ensures that DMA sees correct descriptors
>> >         */
>> OK
>>
>> >> +     wmb();
>> >> +     omap_start_dma(lch);
>> >> +
>> >> +     /* Maintain the pause state in descriptor */
>> >> +     omap_set_dma_sglist_pausebit(lcfg, lcfg->pausenode, 0);
>> >> +     omap_set_dma_sglist_pausebit(lcfg, pauseafter, 1);
>> >> +
>> >> +     /**
>> >> +      * Barrier needed as writes to the
>> >> +      * descriptor memory needs to be flushed
>> >> +      * before it's used by DMA controller
>> >> +      */
>> > Description change if possible
>> OK
>>
>> >> +     wmb();
>> >> +
>> >> +     /* Errata i557 - pausebit should be cleared in no standby mode */
>> > This should have been
>>
>> I couldn't understand this comment.
> This should have been a separate patch since it's an errata.

OK.

>>
>> >> +     sys_cf = dma_read(OCP_SYSCONFIG);
>> >> +     l = sys_cf;
>> >> +     /* Middle mode reg set no Standby */
>> >> +     l &= ~(BIT(12) | BIT(13));
>> >> +     dma_write(l, OCP_SYSCONFIG);
> --
> To unsubscribe from this list: send the line "unsubscribe linux-mmc" in
> the body of a message to majordomo at vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>