rtc: ds1511: clean up ds1511_nvram_read()/ds1511_nvram_write()

The change removes redundant sysfs binary file boundary checks, since
this task is already done on caller side in fs/sysfs/file.c

The change enables burst mode of access to SRAM for any read()/write()
operations, it is worth to mention that this may influence on
userspace, for instance prior to the change

  read(fd, buf, 1);
  read(fd, buf + 1, 1);

and

  read(fd, buf, 2);

sequences of syscalls over DS1511's sysfs "nvram" fd led to different
DS1511 state changes and/or buf content, if some userspace applications
are written specifically for DS1511 and exploit this strange
"feature", they may be impacted.

Also the change corrects NVRAM size accessible to userspace from 255
bytes to 256 bytes.

Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

1 files changed, 5 insertions, 37 deletions

diff --git a/drivers/rtc/rtc-ds1511.c b/drivers/rtc/rtc-ds1511.c
index 7415c2b4d6e8..da3d04ce83bd 100644
--- a/drivers/rtc/rtc-ds1511.c
+++ b/drivers/rtc/rtc-ds1511.c
@@ -64,7 +64,7 @@ enum ds1511reg {
 #define DS1511_KIE      0x04
 #define DS1511_WDE      0x02
 #define DS1511_WDS      0x01
-#define DS1511_RAM_MAX  0xff
+#define DS1511_RAM_MAX  0x100
 
 #define RTC_CMD         DS1511_CONTROL_B
 #define RTC_CMD1        DS1511_CONTROL_A
@@ -159,7 +159,7 @@ ds1511_wdog_set(unsigned long deciseconds)
         /*
          * set wdog enable and wdog 'steering' bit to issue a reset
          */
-        rtc_write(DS1511_WDE | DS1511_WDS, RTC_CMD);
+        rtc_write(rtc_read(RTC_CMD) | DS1511_WDE | DS1511_WDS, RTC_CMD);
 }
 
 void
@@ -407,26 +407,10 @@ ds1511_nvram_read(struct file *filp, struct kobject *kobj,
 {
         ssize_t count;
 
-        /*
-         * if count is more than one, turn on "burst" mode
-         * turn it off when you're done
-         */
-        if (size > 1)
-                rtc_write((rtc_read(RTC_CMD) | DS1511_BME), RTC_CMD);
-
-        if (pos > DS1511_RAM_MAX)
-                pos = DS1511_RAM_MAX;
-
-        if (size + pos > DS1511_RAM_MAX + 1)
-                size = DS1511_RAM_MAX - pos + 1;
-
         rtc_write(pos, DS1511_RAMADDR_LSB);
-        for (count = 0; size > 0; count++, size--)
+        for (count = 0; count < size; count++)
                 *buf++ = rtc_read(DS1511_RAMDATA);
 
-        if (count > 1)
-                rtc_write((rtc_read(RTC_CMD) & ~DS1511_BME), RTC_CMD);
-
         return count;
 }
 
@@ -437,26 +421,10 @@ ds1511_nvram_write(struct file *filp, struct kobject *kobj,
 {
         ssize_t count;
 
-        /*
-         * if count is more than one, turn on "burst" mode
-         * turn it off when you're done
-         */
-        if (size > 1)
-                rtc_write((rtc_read(RTC_CMD) | DS1511_BME), RTC_CMD);
-
-        if (pos > DS1511_RAM_MAX)
-                pos = DS1511_RAM_MAX;
-
-        if (size + pos > DS1511_RAM_MAX + 1)
-                size = DS1511_RAM_MAX - pos + 1;
-
         rtc_write(pos, DS1511_RAMADDR_LSB);
-        for (count = 0; size > 0; count++, size--)
+        for (count = 0; count < size; count++)
                 rtc_write(*buf++, DS1511_RAMDATA);
 
-        if (count > 1)
-                rtc_write((rtc_read(RTC_CMD) & ~DS1511_BME), RTC_CMD);
-
         return count;
 }
 
@@ -490,7 +458,7 @@ static int ds1511_rtc_probe(struct platform_device *pdev)
         /*
          * turn on the clock and the crystal, etc.
          */
-        rtc_write(0, RTC_CMD);
+        rtc_write(DS1511_BME, RTC_CMD);
         rtc_write(0, RTC_CMD1);
         /*
          * clear the wdog counter