[U-Boot] [PATCH RESEND 1/7] spi: cadence_qspi: remove sram polling from flash read

Vikas Manocha
2015-06-17T02:14:19Z

There is no need to check for sram fill level. If sram is empty, cpu
will go in the wait state till the time data is available from flash.

Also Relying on SRAM fill level only for deciding when the data should be
fetched from the local SRAM is not most efficient approach, particulary
if we are working on high data rates.

It should be noticed that after one SRAM word is collected, the information is
forwarded into system domain and then synchronized into register domain (apb).
If we are using slow APB and AHB clks, SRAM fill level might not be up-to-dated
because of latency cycles needed for synchronization. For example in case we are
getting SRAM fill level equal to 10 locations but in reality there were 2
another words completed and actual level is 12 but information may not be
synchronized yet because of the synchronization latency on APB domain.

Signed-off-by: Vikas Manocha <vikas.manocha@st.com>
---
drivers/spi/cadence_qspi_apb.c | 45 +++++-----------------------------------
1 file changed, 5 insertions(+), 40 deletions(-)

diff --git a/drivers/spi/cadence_qspi_apb.c b/drivers/spi/cadence_qspi_apb.c
index 00a115f..8eeb423 100644
--- a/drivers/spi/cadence_qspi_apb.c
+++ b/drivers/spi/cadence_qspi_apb.c
@@ -198,7 +198,7 @@ static unsigned int cadence_qspi_apb_cmd2addr(const unsigned char *addr_buf,
return addr;
}

-static void cadence_qspi_apb_read_fifo_data(void *dest,
+static int cadence_qspi_apb_read_fifo_data(void *dest,
const void *src_ahb_addr, unsigned int bytes)
{
unsigned int temp;
@@ -219,7 +219,7 @@ static void cadence_qspi_apb_read_fifo_data(void *dest,
dest_ptr++;
}

- return;
+ return 0;
}

static void cadence_qspi_apb_write_fifo_data(const void *dest_ahb_addr,
@@ -246,42 +246,6 @@ static void cadence_qspi_apb_write_fifo_data(const void *dest_ahb_addr,
return;
}

-/* Read from SRAM FIFO with polling SRAM fill level. */
-static int qspi_read_sram_fifo_poll(const void *reg_base, void *dest_addr,
- const void *src_addr, unsigned int num_bytes)
-{
- unsigned int remaining = num_bytes;
- unsigned int retry;
- unsigned int sram_level = 0;
- unsigned char *dest = (unsigned char *)dest_addr;
-
- while (remaining > 0) {
- retry = CQSPI_REG_RETRY;
- while (retry--) {
- sram_level = CQSPI_GET_RD_SRAM_LEVEL(reg_base);
- if (sram_level)
- break;
- udelay(1);
- }
-
- if (!retry) {
- printf("QSPI: No receive data after polling for %d times\n",
- CQSPI_REG_RETRY);
- return -1;
- }
-
- sram_level *= CQSPI_FIFO_WIDTH;
- sram_level = sram_level > remaining ? remaining : sram_level;
-
- /* Read data from FIFO. */
- cadence_qspi_apb_read_fifo_data(dest, src_addr, sram_level);
- dest += sram_level;
- remaining -= sram_level;
- udelay(1);
- }
- return 0;
-}
-
/* Write to SRAM FIFO with polling SRAM fill level. */
static int qpsi_write_sram_fifo_push(struct cadence_spi_platdata *plat,
const void *src_addr, unsigned int num_bytes)
@@ -759,9 +723,10 @@ int cadence_qspi_apb_indirect_read_execute(struct cadence_spi_platdata *plat,
/* Start the indirect read transfer */
writel(CQSPI_REG_INDIRECTRD_START_MASK,
plat->regbase + CQSPI_REG_INDIRECTRD);
+ udelay(1);

- if (qspi_read_sram_fifo_poll(plat->regbase, (void *)rxbuf,
- (const void *)plat->ahbbase, rxlen))
+ if (cadence_qspi_apb_read_fifo_data((void *)rxbuf,
+ (const void *)plat->ahbbase, rxlen))
goto failrd;

/* Check flash indirect controller */
--
1.7.9.5