Re: [PATCH 2/3] [v2] m68k: mac: use time64_t in RTC handling

[Finn Thain]

On Tue, 19 Jun 2018, Arnd Bergmann wrote:

> The real-time clock on m68k (and powerpc) mac systems uses an unsigned 
> 32-bit value starting in 1904, which overflows in 2040, about two years 
> later than everyone else, but this gets wrapped around in the Linux code 
> in 2038 already because of the deprecated usage of time_t and/or long in 
> the conversion.
> 
> Getting rid of the deprecated interfaces makes it work until 2040 as 
> documented, and it could be easily extended by reinterpreting the 
> resulting time64_t as a positive number. For the moment, I'm adding a 
> WARN_ON() that triggers if we encounter a time before 1970 or after 2040 
> (the two are indistinguishable).
> 

I really don't like the WARN_ON(), but I'd prefer to address that in a 
separate patch rather than impede the progress of this patch (or of this 
series, since 3/3 seems to be unrelated).

BTW, have you considered using the same wrap-around test (i.e. YY < 70) 
that we use for the year register in the other RTC chips?

> This brings it in line with the corresponding code that we have on 
> powerpc macintosh.
> 

Your recent patches to the Mac RTC routines (which are duplicated under 
arch/m68k and arch/powerpc) conflict with my recent patch that 
deduplicates the same code. So I will rebase and resubmit after someone 
merges these fixes.

Apparently the PowerMac routines work now, which is sufficient testing for 
me; the PowerMac routines will get tested on m68k Macs when that code gets 
deduplicated again.

BTW, Joshua tells me that he is not doing code review. We should probably 
drop the "M68K ON APPLE MACINTOSH" entry from the MAINTAINERS file, like 
the Amiga and Atari ports...

-- 

> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
> v2: Fix varargs passing bug pointed out by Andreas Schwab
>     Fix a typo that caused a build regression
> ---
>  arch/m68k/mac/misc.c | 62 +++++++++++++++++++++++++++++++++-------------------
>  1 file changed, 39 insertions(+), 23 deletions(-)
> 
> diff --git a/arch/m68k/mac/misc.c b/arch/m68k/mac/misc.c
> index c68054361615..0a2572a6bfe5 100644
> --- a/arch/m68k/mac/misc.c
> +++ b/arch/m68k/mac/misc.c
> @@ -26,33 +26,39 @@
>  
>  #include <asm/machdep.h>
>  
> -/* Offset between Unix time (1970-based) and Mac time (1904-based) */
> +/* Offset between Unix time (1970-based) and Mac time (1904-based). Cuda and PMU
> + * times wrap in 2040. If we need to handle later times, the read_time functions
> + * need to be changed to interpret wrapped times as post-2040. */
>  
>  #define RTC_OFFSET 2082844800
>  
>  static void (*rom_reset)(void);
>  
>  #ifdef CONFIG_ADB_CUDA
> -static long cuda_read_time(void)
> +static time64_t cuda_read_time(void)
>  {
>  	struct adb_request req;
> -	long time;
> +	time64_t time;
>  
>  	if (cuda_request(&req, NULL, 2, CUDA_PACKET, CUDA_GET_TIME) < 0)
>  		return 0;
>  	while (!req.complete)
>  		cuda_poll();
>  
> -	time = (req.reply[3] << 24) | (req.reply[4] << 16) |
> -	       (req.reply[5] << 8) | req.reply[6];
> +	time = (u32)((req.reply[3] << 24) | (req.reply[4] << 16) |
> +		     (req.reply[5] << 8) | req.reply[6]);
> +
> +	/* it's either after year 2040, or the RTC has gone backwards */
> +	WARN_ON(time < RTC_OFFSET);
> +
>  	return time - RTC_OFFSET;
>  }
>  
> -static void cuda_write_time(long data)
> +static void cuda_write_time(time64_t time)
>  {
>  	struct adb_request req;
> +	u32 data = lower_32_bits(time + RTC_OFFSET);
>  
> -	data += RTC_OFFSET;
>  	if (cuda_request(&req, NULL, 6, CUDA_PACKET, CUDA_SET_TIME,
>  			 (data >> 24) & 0xFF, (data >> 16) & 0xFF,
>  			 (data >> 8) & 0xFF, data & 0xFF) < 0)
> @@ -86,26 +92,30 @@ static void cuda_write_pram(int offset, __u8 data)
>  #endif /* CONFIG_ADB_CUDA */
>  
>  #ifdef CONFIG_ADB_PMU68K
> -static long pmu_read_time(void)
> +static time64_t pmu_read_time(void)
>  {
>  	struct adb_request req;
> -	long time;
> +	time64_t time;
>  
>  	if (pmu_request(&req, NULL, 1, PMU_READ_RTC) < 0)
>  		return 0;
>  	while (!req.complete)
>  		pmu_poll();
>  
> -	time = (req.reply[1] << 24) | (req.reply[2] << 16) |
> -	       (req.reply[3] << 8) | req.reply[4];
> +	time = (u32)((req.reply[1] << 24) | (req.reply[2] << 16) |
> +		     (req.reply[3] << 8) | req.reply[4]);
> +
> +	/* it's either after year 2040, or the RTC has gone backwards */
> +	WARN_ON(time < RTC_OFFSET);
> +
>  	return time - RTC_OFFSET;
>  }
>  
> -static void pmu_write_time(long data)
> +static void pmu_write_time(time64_t time)
>  {
>  	struct adb_request req;
> +	u32 data = lower_32_bits(time + RTC_OFFSET);
>  
> -	data += RTC_OFFSET;
>  	if (pmu_request(&req, NULL, 5, PMU_SET_RTC,
>  			(data >> 24) & 0xFF, (data >> 16) & 0xFF,
>  			(data >> 8) & 0xFF, data & 0xFF) < 0)
> @@ -269,8 +279,12 @@ static long via_read_time(void)
>  		via_pram_command(0x89, &result.cdata[1]);
>  		via_pram_command(0x8D, &result.cdata[0]);
>  
> -		if (result.idata == last_result.idata)
> +		if (result.idata == last_result.idata) {
> +			if (result.idata < RTC_OFFSET)
> +				result.idata += 0x100000000ull;
> +
>  			return result.idata - RTC_OFFSET;
> +		}
>  
>  		if (++count > 10)
>  			break;
> @@ -291,11 +305,11 @@ static long via_read_time(void)
>   * is basically any machine with Mac II-style ADB.
>   */
>  
> -static void via_write_time(long time)
> +static void via_write_time(time64_t time)
>  {
>  	union {
>  		__u8 cdata[4];
> -		long idata;
> +		__u32 idata;
>  	} data;
>  	__u8 temp;
>  
> @@ -585,12 +599,15 @@ void mac_reset(void)
>   * This function translates seconds since 1970 into a proper date.
>   *
>   * Algorithm cribbed from glibc2.1, __offtime().
> + *
> + * This is roughly same as rtc_time64_to_tm(), which we should probably
> + * use here, but it's only available when CONFIG_RTC_LIB is enabled.
>   */
>  #define SECS_PER_MINUTE (60)
>  #define SECS_PER_HOUR  (SECS_PER_MINUTE * 60)
>  #define SECS_PER_DAY   (SECS_PER_HOUR * 24)
>  
> -static void unmktime(unsigned long time, long offset,
> +static void unmktime(time64_t time, long offset,
>  		     int *yearp, int *monp, int *dayp,
>  		     int *hourp, int *minp, int *secp)
>  {
> @@ -602,11 +619,10 @@ static void unmktime(unsigned long time, long offset,
>  		/* Leap years.  */
>  		{ 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 }
>  	};
> -	long int days, rem, y, wday, yday;
> +	int days, rem, y, wday, yday;
>  	const unsigned short int *ip;
>  
> -	days = time / SECS_PER_DAY;
> -	rem = time % SECS_PER_DAY;
> +	days = div_u64_rem(time, SECS_PER_DAY, &rem);
>  	rem += offset;
>  	while (rem < 0) {
>  		rem += SECS_PER_DAY;
> @@ -657,7 +673,7 @@ static void unmktime(unsigned long time, long offset,
>  
>  int mac_hwclk(int op, struct rtc_time *t)
>  {
> -	unsigned long now;
> +	time64_t now;
>  
>  	if (!op) { /* read */
>  		switch (macintosh_config->adb_type) {
> @@ -693,8 +709,8 @@ int mac_hwclk(int op, struct rtc_time *t)
>  		         __func__, t->tm_year + 1900, t->tm_mon + 1, t->tm_mday,
>  		         t->tm_hour, t->tm_min, t->tm_sec);
>  
> -		now = mktime(t->tm_year + 1900, t->tm_mon + 1, t->tm_mday,
> -			     t->tm_hour, t->tm_min, t->tm_sec);
> +		now = mktime64(t->tm_year + 1900, t->tm_mon + 1, t->tm_mday,
> +			       t->tm_hour, t->tm_min, t->tm_sec);
>  
>  		switch (macintosh_config->adb_type) {
>  		case MAC_ADB_IOP:
>