Re: [PATCH 15/16] fpga: machxo2: extend erase timeout for machxo2 FPGA

On 2022-08-29 at 12:51:19 +0200, Johannes Zink wrote:

Hi Yilun, 

On Mon, 2022-08-29 at 17:26 +0800, Xu Yilun wrote:

quoted

On 2022-08-25 at 16:13:42 +0200, Johannes Zink wrote:

quoted

Measurements showed that some FPGAs take significantly longer than
the
default wait function supplied. The datasheet inidicates up to 30
seconds erase times for some MachXO2 FPGAs, depending on the number
of
LUTs (and the corresponding configuration flash size).

Signed-off-by: Johannes Zink <redacted>
---
 drivers/fpga/machxo2-common.c | 28 ++++++++++++++++++++++++++--
 1 file changed, 26 insertions(+), 2 deletions(-)

diff --git a/drivers/fpga/machxo2-common.c b/drivers/fpga/machxo2-

common.c
index ccf9a50fc590..e8967cdee2c6 100644

--- a/drivers/fpga/machxo2-common.c
+++ b/drivers/fpga/machxo2-common.c

@@ -17,6 +17,8 @@

 #include <linux/module.h>
 #include <linux/of.h>
 #include <linux/property.h>
+#include <linux/iopoll.h>
+#include <linux/time.h>
 #include "machxo2-common.h"
 
 #define MACHXO2_LOW_DELAY_USEC          5

@@ -24,6 +26,8 @@

 #define MACHXO2_REFRESH_USEC            4800
 #define MACHXO2_MAX_BUSY_LOOP           128
 #define MACHXO2_MAX_REFRESH_LOOP        16
+#define MACHXO2_MAX_ERASE_USEC          (30 * USEC_PER_SEC)
+#define MACHXO2_ERASE_USEC_SLEEP        (20 * USEC_PER_MSEC)
 
 #define MACHXO2_PAGE_SIZE               16
 #define MACHXO2_BUF_SIZE                (MACHXO2_PAGE_SIZE + 4)

@@ -54,6 +58,18 @@

 #define ISC_ERASE_FEATURE_ROW  BIT(17)
 #define ISC_ERASE_UFM          BIT(19)
 
+static inline int machxo2_wait_until_not_busy_timeout(struct
machxo2_common_priv *priv)
+{
+       int ret, pollret;
+       u32 status = MACHXO2_BUSY;
+
+       pollret = read_poll_timeout(priv->get_status, ret,
+                                   (ret && ret != -EAGAIN) ||
!(status & MACHXO2_BUSY),
+                                   MACHXO2_ERASE_USEC_SLEEP,
MACHXO2_MAX_ERASE_USEC,
+                                   true, priv, &status);

Why just taking care of erase timeout? I see the busy wait in many
places.

Erasing the flash memory takes significantly longer than the other
operations (up to 30s), which is why I decided to use this separate
implementation. For other commands the fpga indicates no-more-busy much
faster than for the erase_flash command.

It is almost always better to have a relatively measureable timeout,
unless it is really time critical. Apparently spi/i2c transfer is not
time critical itself. So since you have implemented a better function,
why not use it?

Thanks,
Yilun

quoted

quoted

+
+       return ret ?: pollret;
+}
 
 static inline u8 get_err(u32 status)
 {

@@ -114,6 +130,12 @@ static int machxo2_cleanup(struct fpga_manager

*mgr)
        if (ret)
                goto fail;
 
+       ret = machxo2_wait_until_not_busy_timeout(priv);
+       if (ret) {
+               dev_err(&mgr->dev, "Erase operation failed (%d)",
ret);
+               goto fail;
+       }
+
        ret = machxo2_wait_until_not_busy(priv);

Is this line still needed?

agreed, this line should become obsolete, since if we reach this point
the fpga is not indicating busy any longer or the wait has been aborted
due to an error. I will remove it in v2.

quoted

quoted

        if (ret)
                goto fail;

@@ -192,9 +214,11 @@ static int machxo2_write_init(struct

fpga_manager *mgr,
        if (ret)
                goto fail;
 
-       ret = machxo2_wait_until_not_busy(priv);
-       if (ret)
+       ret = machxo2_wait_until_not_busy_timeout(priv);
+       if (ret) {
+               dev_err(&mgr->dev, "Erase operation failed (%d)",
ret);
                goto fail;
+       }
 
        priv->get_status(priv, &status);
        if (status & MACHXO2_FAIL) {
-- 
2.30.2

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