Hi Huang,
Sorry to address this series so late.
I have a few questions about how you determine support for these DDR
modes.
On Mon, Apr 28, 2014 at 11:53:40AM +0800, Huang Shijie wrote:
> This patch adds the DDR quad read support by the following:
To Mark / linux-spi:
Are DDR modes in the scope of drivers/spi/ at all, so that we could
someday wire it up through m25p80.c? Or is 'DDR' such a distortion of
the meaning of 'SPI' such that it will be restricted only to SPI NOR
dedicated controllers?
> [1] add SPI_NOR_DDR_QUAD read mode.
>
> [2] add DDR Quad read opcodes:
> SPINOR_OP_READ_1_4_4_D / SPINOR_OP_READ4_1_4_4_D
>
> [3] add set_ddr_quad_mode() to initialize for the DDR quad read.
> Currently it only works for Spansion NOR.
>
> [3] about the dummy cycles.
> We set the dummy with 8 for DDR quad read by default.
Why? That seems wrong. You need to know for sure how many cycles should
be used, not just guess a default.
> The m25p80.c can not support the DDR quad read, but the SPI NOR
> controller
> can set the dummy value in its child DT node, and the SPI NOR framework
> can parse it out.
Why does the dummy value belong in device tree? I think this can be
handled in software. You might, however, want a few other hardware
description parameters in device tree to help you.
So I think spi-nor.c needs to know a few things:
1. Does the hardware/driver support DDR clocking?
2. What granularity of dummy cycles are supported? So m25p80.c needs to
communicate that it only supports dummy cycles of multiples of 8,
and fsl-quadspi supports single clock cycles.
And spi-nor.c should be able to do the following:
3. Set how many dummy cycles should be used.
4. Write to the configuration register, to choose a Latency Code
according to what the flash supports. I see modes that support 3, 6,
7, or 8. We'd probably just go for the fastest mode, which requires
8, right?
So far, none of this seems to require a DT binding, unless there's
something I'm missing about your fsl-quadspi controller.
> Test this patch for Spansion s25fl128s NOR flash.
>
> Signed-off-by: Huang Shijie <[email protected]>
> ---
> drivers/mtd/spi-nor/spi-nor.c | 54 +++++++++++++++++++++++++++++++++++++++-
> include/linux/mtd/spi-nor.h | 8 ++++-
> 2 files changed, 58 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
> index f374e44..e0bc11a 100644
> --- a/drivers/mtd/spi-nor/spi-nor.c
> +++ b/drivers/mtd/spi-nor/spi-nor.c
> @@ -73,7 +73,20 @@ static int read_cr(struct spi_nor *nor)
> */
> static inline int spi_nor_read_dummy_cycles(struct spi_nor *nor)
> {
> + u32 dummy;
> +
> switch (nor->flash_read) {
> + case SPI_NOR_DDR_QUAD:
> + /*
> + * The m25p80.c can not support the DDR quad read.
> + * We set the dummy cycles to 8 by default. The SPI NOR
> + * controller driver can set it in its child DT node.
> + * We parse it out here.
> + */
> + if (nor->np && !of_property_read_u32(nor->np,
> + "spi-nor,ddr-quad-read-dummy", &dummy)) {
> + return dummy;
> + }
> case SPI_NOR_FAST:
> case SPI_NOR_DUAL:
> case SPI_NOR_QUAD:
> @@ -402,6 +415,7 @@ struct flash_info {
> #define SECT_4K_PMC 0x10 /* SPINOR_OP_BE_4K_PMC works
> uniformly */
> #define SPI_NOR_DUAL_READ 0x20 /* Flash supports Dual Read */
> #define SPI_NOR_QUAD_READ 0x40 /* Flash supports Quad Read */
> +#define SPI_NOR_DDR_QUAD_READ 0x80 /* Flash supports DDR Quad Read
> */
> };
>
> #define INFO(_jedec_id, _ext_id, _sector_size, _n_sectors, _flags) \
> @@ -846,6 +860,24 @@ static int spansion_quad_enable(struct spi_nor *nor)
> return 0;
> }
>
> +static int set_ddr_quad_mode(struct spi_nor *nor, u32 jedec_id)
> +{
> + int status;
> +
> + switch (JEDEC_MFR(jedec_id)) {
> + case CFI_MFR_AMD: /* Spansion, actually */
> + status = spansion_quad_enable(nor);
> + if (status) {
> + dev_err(nor->dev,
> + "Spansion DDR quad-read not enabled\n");
> + return status;
> + }
> + return status;
> + default:
> + return -EINVAL;
> + }
> +}
> +
> static int set_quad_mode(struct spi_nor *nor, u32 jedec_id)
> {
> int status;
> @@ -1016,8 +1048,15 @@ int spi_nor_scan(struct spi_nor *nor, const struct
> spi_device_id *id,
> if (info->flags & SPI_NOR_NO_FR)
> nor->flash_read = SPI_NOR_NORMAL;
>
> - /* Quad/Dual-read mode takes precedence over fast/normal */
> - if (mode == SPI_NOR_QUAD && info->flags & SPI_NOR_QUAD_READ) {
> + /* DDR Quad/Quad/Dual-read mode takes precedence over fast/normal */
> + if (mode == SPI_NOR_DDR_QUAD && info->flags & SPI_NOR_DDR_QUAD_READ) {
Hmm, I think I should probably take another look at the design of
spi-nor.c... Why does spi_nor_scan() take a single 'mode' argument? The
driver should be communicating which (multiple) modes it supports, not
selecting a single mode. spi-nor.c is the only one which knows what the
*flash* supports, so it should be combining knowledge from the
controller driver with its own knowledge of the flash.
> + ret = set_ddr_quad_mode(nor, info->jedec_id);
> + if (ret) {
> + dev_err(dev, "DDR quad mode not supported\n");
> + return ret;
A ramification of my comment above is that we should not be returning an
error in a situation like this; we should be able to fall back to
another known-supported mode, like SDR QUAD, SDR DUAL, or just plain
SPI -- if they're supported by the driver -- and spi-nor.c doesn't
currently have enough information to do this.
> + }
> + nor->flash_read = SPI_NOR_DDR_QUAD;
> + } else if (mode == SPI_NOR_QUAD && info->flags & SPI_NOR_QUAD_READ) {
> ret = set_quad_mode(nor, info->jedec_id);
> if (ret) {
> dev_err(dev, "quad mode not supported\n");
> @@ -1030,6 +1069,14 @@ int spi_nor_scan(struct spi_nor *nor, const struct
> spi_device_id *id,
>
> /* Default commands */
> switch (nor->flash_read) {
> + case SPI_NOR_DDR_QUAD:
> + if (JEDEC_MFR(info->jedec_id) == CFI_MFR_AMD) { /* Spansion */
> + nor->read_opcode = SPINOR_OP_READ_1_4_4_D;
> + } else {
> + dev_err(dev, "DDR Quad Read is not supported.\n");
> + return -EINVAL;
> + }
> + break;
> case SPI_NOR_QUAD:
> nor->read_opcode = SPINOR_OP_READ_1_1_4;
> break;
> @@ -1057,6 +1104,9 @@ int spi_nor_scan(struct spi_nor *nor, const struct
> spi_device_id *id,
> if (JEDEC_MFR(info->jedec_id) == CFI_MFR_AMD) {
> /* Dedicated 4-byte command set */
> switch (nor->flash_read) {
> + case SPI_NOR_DDR_QUAD:
> + nor->read_opcode = SPINOR_OP_READ4_1_4_4_D;
> + break;
> case SPI_NOR_QUAD:
> nor->read_opcode = SPINOR_OP_READ4_1_1_4;
> break;
> diff --git a/include/linux/mtd/spi-nor.h b/include/linux/mtd/spi-nor.h
> index 48fe9fc..d191a6b 100644
> --- a/include/linux/mtd/spi-nor.h
> +++ b/include/linux/mtd/spi-nor.h
> @@ -12,10 +12,11 @@
>
> /*
> * Note on opcode nomenclature: some opcodes have a format like
> - * SPINOR_OP_FUNCTION{4,}_x_y_z. The numbers x, y, and z stand for the number
> + * SPINOR_OP_FUNCTION{4,}_x_y_z{_D}. The numbers x, y, and z stand for the
> number
> * of I/O lines used for the opcode, address, and data (respectively). The
> * FUNCTION has an optional suffix of '4', to represent an opcode which
> - * requires a 4-byte (32-bit) address.
> + * requires a 4-byte (32-bit) address. The suffix of 'D' stands for the
> + * DDR mode.
> */
>
> /* Flash opcodes. */
> @@ -26,6 +27,7 @@
> #define SPINOR_OP_READ_FAST 0x0b /* Read data bytes (high frequency) */
> #define SPINOR_OP_READ_1_1_2 0x3b /* Read data bytes (Dual SPI) */
> #define SPINOR_OP_READ_1_1_4 0x6b /* Read data bytes (Quad SPI) */
> +#define SPINOR_OP_READ_1_4_4_D 0xed /* Read data bytes (DDR Quad
> SPI) */
> #define SPINOR_OP_PP 0x02 /* Page program (up to 256 bytes) */
> #define SPINOR_OP_BE_4K 0x20 /* Erase 4KiB block */
> #define SPINOR_OP_BE_4K_PMC 0xd7 /* Erase 4KiB block on PMC chips */
> @@ -40,6 +42,7 @@
> #define SPINOR_OP_READ4_FAST 0x0c /* Read data bytes (high frequency) */
> #define SPINOR_OP_READ4_1_1_2 0x3c /* Read data bytes (Dual SPI) */
> #define SPINOR_OP_READ4_1_1_4 0x6c /* Read data bytes (Quad SPI) */
> +#define SPINOR_OP_READ4_1_4_4_D 0xee /* Read data bytes (DDR Quad
> SPI) */
> #define SPINOR_OP_PP_4B 0x12 /* Page program (up to 256
> bytes) */
> #define SPINOR_OP_SE_4B 0xdc /* Sector erase (usually 64KiB)
> */
>
> @@ -74,6 +77,7 @@ enum read_mode {
> SPI_NOR_FAST,
> SPI_NOR_DUAL,
> SPI_NOR_QUAD,
> + SPI_NOR_DDR_QUAD,
> };
>
> /**
So, I'll have to take another hard look at spi-nor.c soon. I think we
may need to work on the abstractions here a bit more before I merge any
new features like this.
Regards,
Brian
P.S. Is there a good reason we've defined a whole read_xfer/write_xfer
API that is completely unused?
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