Re: [PATCH] applesmc: Re-work SMC comms v2

Brad Campbell
2020-11-06T00:03:47Z

On 6/11/20 3:12 am, Guenter Roeck wrote:
> On 11/4/20 11:26 PM, Brad Campbell wrote:
>> Commit fff2d0f701e6 ("hwmon: (applesmc) avoid overlong udelay()") introduced
>> an issue whereby communication with the SMC became unreliable with write
>> errors like :
>>
>> [ 120.378614] applesmc: send_byte(0x00, 0x0300) fail: 0x40
>> [ 120.378621] applesmc: LKSB: write data fail
>> [ 120.512782] applesmc: send_byte(0x00, 0x0300) fail: 0x40
>> [ 120.512787] applesmc: LKSB: write data fail
>>
>> The original code appeared to be timing sensitive and was not reliable with
>> the timing changes in the aforementioned commit.
>>
>> This patch re-factors the SMC communication to remove the timing
>> dependencies and restore function with the changes previously committed.
>>
>
> Still a few formatting problems, but I like this version. Id take
> care of the formatting myself, but send_command() will need a change.

Nope, I'm more than happy to sort it all out. It's a learning process.

I'd still like this to get some wider testing before I consider it ready to go
so extra revisions don't worry me.

> Subject should be
> [PATCH v<version>] hwmon: (applesmc) ...

Thanks.

>> v2 : Address logic and coding style
>
> Change log should be after '---'

No worries, can do.

>
>>
>> Reported-by: Andreas Kemnade <andreas@kemnade.info>
>> Fixes: fff2d0f701e6 ("hwmon: (applesmc) avoid overlong udelay()")
>> Signed-off-by: Brad Campbell <brad@fnarfbargle.com>
>>
>> ---
>> diff --git a/drivers/hwmon/applesmc.c b/drivers/hwmon/applesmc.c
>> index a18887990f4a..de890f3ec12f 100644
>> --- a/drivers/hwmon/applesmc.c
>> +++ b/drivers/hwmon/applesmc.c
>> @@ -42,6 +42,11 @@
>>
>> #define APPLESMC_MAX_DATA_LENGTH 32
>>
>> +/* Apple SMC status bits */
>> +#define SMC_STATUS_AWAITING_DATA BIT(0) /* SMC has data waiting */
>> +#define SMC_STATUS_IB_CLOSED BIT(1) /* Will ignore any input */
>> +#define SMC_STATUS_BUSY BIT(2) /* Command in progress */
>> +
>
> Hah, tricked you here ;-). Using "BIT()" requires
>
> #include <linux/bits.h>

"requires" ??
It compiles and tests without warning, but I'll certainly add it in.

>> /* wait up to 128 ms for a status change. */
>> #define APPLESMC_MIN_WAIT 0x0010
>> #define APPLESMC_RETRY_WAIT 0x0100
>> @@ -151,65 +156,69 @@ static unsigned int key_at_index;
>> static struct workqueue_struct *applesmc_led_wq;
>>
>> /*
>> - * wait_read - Wait for a byte to appear on SMC port. Callers must
>> - * hold applesmc_lock.
>> + * Wait for specific status bits with a mask on the SMC
>> + * Used before and after writes, and before reads
>> */
>> -static int wait_read(void)
>> +
>> +static int wait_status(u8 val, u8 mask)
>> {
>> unsigned long end = jiffies + (APPLESMC_MAX_WAIT * HZ) / USEC_PER_SEC;
>> u8 status;
>> int us;
>>
>> for (us = APPLESMC_MIN_WAIT; us < APPLESMC_MAX_WAIT; us <<= 1) {
>> - usleep_range(us, us * 16);
>> status = inb(APPLESMC_CMD_PORT);
>> - /* read: wait for smc to settle */
>> - if (status & 0x01)
>> + if ((status & mask) == val)
>> return 0;
>> /* timeout: give up */
>> if (time_after(jiffies, end))
>> break;
>> - }
>> -
>> - pr_warn("wait_read() fail: 0x%02x\n", status);
>> + usleep_range(us, us * 16);
>> + }
>
> Bad indentation of "}"

Yeah, I've found my editor "less than optimal" and I've had to correct a few
tab related indent problems manually. Thanks.

>> return -EIO;
>> }
>>
>> /*
>> - * send_byte - Write to SMC port, retrying when necessary. Callers
>> + * send_byte_data - Write to SMC data port. Callers
>> * must hold applesmc_lock.
>> + * Parameter skip must be true on the last write of any
>> + * command or it'll time out.
>> */
>> -static int send_byte(u8 cmd, u16 port)
>> +
>> +static int send_byte_data(u8 cmd, u16 port, bool skip)
>> {
>> - u8 status;
>> - int us;
>> - unsigned long end = jiffies + (APPLESMC_MAX_WAIT * HZ) / USEC_PER_SEC;
>> + int ret;
>>
>> + ret = wait_status(SMC_STATUS_BUSY, SMC_STATUS_BUSY | SMC_STATUS_IB_CLOSED);
>> + if (ret)
>> + return ret;
>> outb(cmd, port);
>> - for (us = APPLESMC_MIN_WAIT; us < APPLESMC_MAX_WAIT; us <<= 1) {
>> - usleep_range(us, us * 16);
>> - status = inb(APPLESMC_CMD_PORT);
>> - /* write: wait for smc to settle */
>> - if (status & 0x02)
>> - continue;
>> - /* ready: cmd accepted, return */
>> - if (status & 0x04)
>> - return 0;
>> - /* timeout: give up */
>> - if (time_after(jiffies, end))
>> - break;
>> - /* busy: long wait and resend */
>> - udelay(APPLESMC_RETRY_WAIT);
>> - outb(cmd, port);
>> - }
>> + return wait_status(skip ? 0 : SMC_STATUS_BUSY, SMC_STATUS_BUSY);
>> +}
>>
>> - pr_warn("send_byte(0x%02x, 0x%04x) fail: 0x%02x\n", cmd, port, status);
>> - return -EIO;
>> +static int send_byte(u8 cmd, u16 port)
>> +{
>> + return send_byte_data(cmd, port, false);
>> }
>>
>> +/*
>> + * send_command - Write a command to the SMC. Callers must hold applesmc_lock.
>> + * If SMC is in undefined state, any new command write resets the state machine.
>> + */
>> +
>> static int send_command(u8 cmd)
>> {
>> - return send_byte(cmd, APPLESMC_CMD_PORT);
>> + u8 status;
>> + int ret;
>> +
>> + ret = wait_status(0, SMC_STATUS_IB_CLOSED);
>> + if (ret)
>> + return ret;
>> +
>> + status = inb(APPLESMC_CMD_PORT);
>> +
>
> Is this read necessary ? 'status' isn't used subsequently, meaning we'll
> probably get static analyzer warnings about a variable which is assigned
> but unused. If the read is necessary, just don't assign it to a variable.

No it's not. It's hangover from incompletely remove debug statements.
Henrik Rydberg picked that one up yesterday.

>> + outb(cmd, APPLESMC_CMD_PORT);
>> + return wait_status(SMC_STATUS_BUSY, SMC_STATUS_BUSY);
>> }
>>
>> static int send_argument(const char *key)
>> @@ -239,7 +248,9 @@ static int read_smc(u8 cmd, const char *key, u8 *buffer, u8 len)
>> }
>>
>> for (i = 0; i < len; i++) {
>> - if (wait_read()) {
>> + if (wait_status(SMC_STATUS_AWAITING_DATA | SMC_STATUS_BUSY,
>> + SMC_STATUS_AWAITING_DATA | SMC_STATUS_BUSY |
>> + SMC_STATUS_IB_CLOSED)) {
>> pr_warn("%.4s: read data[%d] fail\n", key, i);
>> return -EIO;
>> }
>> @@ -250,7 +261,7 @@ static int read_smc(u8 cmd, const char *key, u8 *buffer, u8 len)
>> for (i = 0; i < 16; i++) {
>> udelay(APPLESMC_MIN_WAIT);
>> status = inb(APPLESMC_CMD_PORT);
>> - if (!(status & 0x01))
>> + if (!(status & SMC_STATUS_AWAITING_DATA))
>> break;
>> data = inb(APPLESMC_DATA_PORT);
>> }
>> @@ -275,7 +286,7 @@ static int write_smc(u8 cmd, const char *key, const u8 *buffer, u8 len)
>> }
>>
>> for (i = 0; i < len; i++) {
>> - if (send_byte(buffer[i], APPLESMC_DATA_PORT)) {
>> + if (send_byte_data(buffer[i], APPLESMC_DATA_PORT, i == len - 1)) {
>> pr_warn("%s: write data fail\n", key);
>> return -EIO;
>> }
>>
>
>

I'll get a v3 in when I get some more test results.

Much appreciated.
Regards,
Brad