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From: Sergei Shtylyov on 11 Mar 2010 06:10
Hello.

Sudhakar Rajashekhara wrote:

> On some platforms like DM355, the number of EDMA parameter
> slots available for EDMA_SLOT_ANY usage are few. In such cases,
> if MMC/SD uses 16 slots for each instance of MMC controller,
> then the number of slots available for other modules will be
> very few.
>
> By passing the number of EDMA slots to be used in MMC driver
> from platform data, EDMA slots available for other purposes
> can be controlled.
>
> Signed-off-by: Sudhakar Rajashekhara <sudhakar.raj(a)ti.com>
> ---
> arch/arm/mach-davinci/include/mach/mmc.h | 3 +++
> drivers/mmc/host/davinci_mmc.c | 22 +++++++++++++++-------
> 2 files changed, 18 insertions(+), 7 deletions(-)
>
> diff --git a/arch/arm/mach-davinci/include/mach/mmc.h b/arch/arm/mach-davinci/include/mach/mmc.h
> index 5a85e24..384fc0e 100644
> --- a/arch/arm/mach-davinci/include/mach/mmc.h
> +++ b/arch/arm/mach-davinci/include/mach/mmc.h
> @@ -22,6 +22,9 @@ struct davinci_mmc_config {
>
> /* Version of the MMC/SD controller */
> u8 version;
> +
> + /* Number of sg segments */
> + u32 nr_sg;
>

Why waste 4 bytres if the maximum number is 16?

> diff --git a/drivers/mmc/host/davinci_mmc.c b/drivers/mmc/host/davinci_mmc.c
> index 3bd0ba2..19c050c 100644
> --- a/drivers/mmc/host/davinci_mmc.c
> +++ b/drivers/mmc/host/davinci_mmc.c
> @@ -137,15 +137,15 @@
>
> /*
> * One scatterlist dma "segment" is at most MAX_CCNT rw_threshold units,
> - * and we handle up to NR_SG segments. MMC_BLOCK_BOUNCE kicks in only
> + * and we handle up to MAX_NR_SG segments. MMC_BLOCK_BOUNCE kicks in only
> * for drivers with max_hw_segs == 1, making the segments bigger (64KB)
> - * than the page or two that's otherwise typical. NR_SG == 16 gives at
> - * least the same throughput boost, using EDMA transfer linkage instead
> - * of spending CPU time copying pages.
> + * than the page or two that's otherwise typical. nr_sg (passed from
> + * platform data) == 16 gives at least the same throughput boost, using
> + * EDMA transfer linkage instead of spending CPU time copying pages.
> */
> #define MAX_CCNT ((1 << 16) - 1)
>
> -#define NR_SG 16
> +#define MAX_NR_SG 16
>
> static unsigned rw_threshold = 32;
> module_param(rw_threshold, uint, S_IRUGO);
> @@ -192,7 +192,7 @@ struct mmc_davinci_host {
> struct edmacc_param tx_template;
> struct edmacc_param rx_template;
> unsigned n_link;
> - u32 links[NR_SG - 1];
> + u32 links[MAX_NR_SG - 1];
>
> /* For PIO we walk scatterlists one segment at a time. */
>

> unsigned int sg_len;
> @@ -202,6 +202,8 @@ struct mmc_davinci_host {
> u8 version;
> /* for ns in one cycle calculation */
> unsigned ns_in_one_cycle;
> + /* Number of sg segments */
> + u32 nr_sg;
>

Same question.

WBR, Sergei

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From: Andrew Morton on 15 Mar 2010 17:50
On Fri, 12 Mar 2010 18:04:09 +0530
Sudhakar Rajashekhara <sudhakar.raj(a)ti.com> wrote:

> On some platforms like DM355, the number of EDMA parameter
> slots available for EDMA_SLOT_ANY usage are few. In such cases,
> if MMC/SD uses 16 slots for each instance of MMC controller,
> then the number of slots available for other modules will be
> very few.
>
> By passing the number of EDMA slots to be used in MMC driver
> from platform data, EDMA slots available for other purposes
> can be controlled.

It's unclear what the runtime effects of this change are. I assumed
(without justification) that they're minor and I scheduled the patch for
2.6.35.

If that was the wrong decision then blame the changelog ;)
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