Re: [PATCH 03/03] omap hsmmc: adaptation of sdma descriptor autoloading feature

Venkatraman S
2010-03-11T15:08:06Z

Tony Lindgren wrote:
> * Venkatraman S <svenkatr@ti.com> [100310 06:08]:
>> @@ -1400,14 +1471,23 @@ omap_hsmmc_prepare_data(struct omap_hsmmc_host
>> *host, struct mmc_request *req)
>>                                       | (req->data->blocks << 16));
>>       set_data_timeout(host, req->data->timeout_ns, req->data->timeout_clks);
>>
>> -     if (host->use_dma) {
>> -             ret = omap_hsmmc_start_dma_transfer(host, req);
>> -             if (ret != 0) {
>> -                     dev_dbg(mmc_dev(host->mmc), "MMC start dma failure\n");
>> +     if (host->dma_caps & DMA_TYPE_SDMA) {
>> +             ret = omap_hsmmc_configure_sdma(host, req);
>> +             if (ret)
>>                       return ret;
>> -             }
>> +             host->dma_in_use = DMA_TYPE_SDMA;
>>       }
>> -     return 0;
>> +     if ((host->dma_caps & DMA_TYPE_SDMA_DLOAD) &&
>> +             host->data->sg_len > 4) {
>> +             ret = omap_hsmmc_configure_sdma_sglist(host, req);
>> +             if (ret)
>> +                     return ret;
>> +             host->dma_in_use = DMA_TYPE_SDMA_DLOAD;
>> +
>> +     }
>> +     ret = omap_hsmmc_start_dma_transfer(host);
>> +     return ret;
>> +
>>  }
>
> Does the driver still work in PIO mode?
>
> We need to have the drivers capable to fail over to PIO mode
> as the DMA channels can run out.
>

The driver doesn't have an automatic fallback to PIO,
even without my patch. A error return from omap_request_dma is
propogated all the way back to the transfer request.
The decision to use_dma (the variable) is unaltered.

Infact, it would be easier to implement a runtime fallback after
this patch is
merged as I have separated out the capability and runtime selection.
(dma_caps and dma_in_use).

Regards,

Venkat.
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