Message-ID: <ecdedaf0-a4a4-9881-1068-9f186f7ac6af@baylibre.com>
Date:   Mon, 17 Oct 2016 10:25:29 +0200
From:   Neil Armstrong <narmstrong@...libre.com>
To:     Sudeep Holla <sudeep.holla@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     linux-amlogic@...ts.infradead.org, khilman@...libre.com,
        heiko@...ech.de, wxt@...k-chips.com, frank.wang@...k-chips.com
Subject: Re: [PATCH v4 2/8] scpi: Add alternative legacy structures, functions
 and macros

On 10/10/2016 04:36 PM, Sudeep Holla wrote:
> Hi Neil,
> 
> Sorry, I could not reply to your response on v3. Anyways I will review v4.
> 
> On 05/10/16 08:33, Neil Armstrong wrote:
>> This patch adds support for the Legacy SCPI protocol in early JUNO versions and
>> shipped Amlogic ARMv8 based SoCs. Some Rockchip SoC are also known to use this
>> version of protocol with extended vendor commands
>> .
>> In order to support the legacy SCPI protocol variant, add back the structures
>> and macros that varies against the final specification.
>> Then add indirection table for legacy commands.
>> Finally Add bitmap field for channel selection since the Legacy protocol mandates to
>> send a selected subset of the commands on the high priority channel instead of the
>> low priority channel.
>>
>> The message sending path differs from the final SCPI procotocol because the
>> Amlogic SCP firmware always reply 1 instead of a special value containing the command
>> byte and replied rx data length.
>> For this reason commands queuing cannot be used and we assume the reply command is
>> the head of the rx_pending list since we ensure sequential command sending with a
>> separate dedicated mutex.
>>
>> Signed-off-by: Neil Armstrong <narmstrong@...libre.com>
>> ---
>>  drivers/firmware/arm_scpi.c | 221 +++++++++++++++++++++++++++++++++++++++-----
>>  1 file changed, 199 insertions(+), 22 deletions(-)
>>
>> diff --git a/drivers/firmware/arm_scpi.c b/drivers/firmware/arm_scpi.c
>> index 498afa0..6244eb1 100644
>> --- a/drivers/firmware/arm_scpi.c
>> +++ b/drivers/firmware/arm_scpi.c
> 
> [...]
> 
>> @@ -307,21 +398,46 @@ static void scpi_process_cmd(struct scpi_chan *ch, u32 cmd)
>>          return;
>>      }
>>
>> -    list_for_each_entry(t, &ch->rx_pending, node)
>> -        if (CMD_XTRACT_UNIQ(t->cmd) == CMD_XTRACT_UNIQ(cmd)) {
>> -            list_del(&t->node);
>> -            match = t;
>> -            break;
>> -        }
>> +    /* Command type is not replied by the SCP Firmware in legacy Mode
>> +     * We should consider that command is the head of pending RX commands
>> +     * if the list is not empty. In TX only mode, the list would be empty.
>> +     */
>> +    if (scpi_info->is_legacy) {
>> +        match = list_first_entry(&ch->rx_pending, struct scpi_xfer,
>> +                     node);
>> +        list_del(&match->node);
>> +    } else {
>> +        list_for_each_entry(t, &ch->rx_pending, node)
>> +            if (CMD_XTRACT_UNIQ(t->cmd) == CMD_XTRACT_UNIQ(cmd)) {
>> +                list_del(&t->node);
>> +                match = t;
>> +                break;
>> +            }
>> +    }
>>      /* check if wait_for_completion is in progress or timed-out */
>>      if (match && !completion_done(&match->done)) {
>> -        struct scpi_shared_mem *mem = ch->rx_payload;
>> -        unsigned int len = min(match->rx_len, CMD_SIZE(cmd));
>> +        unsigned int len;
>> +
>> +        if (scpi_info->is_legacy) {
>> +            struct legacy_scpi_shared_mem *mem = ch->rx_payload;
>> +
>> +            /* RX Length is not replied by the lagcy Firmware */
>> +            len = match->rx_len;
>> +
>> +            match->status = le32_to_cpu(mem->status);
>> +            memcpy_fromio(match->rx_buf, mem->payload, len);
> 
> The above 2 seems common to both, no ?

No, the shared_mem structure differs.

> 
>> +        } else {
>> +            struct scpi_shared_mem *mem = ch->rx_payload;
>> +
>> +            len = min(match->rx_len, CMD_SIZE(cmd));
>> +
>> +            match->status = le32_to_cpu(mem->status);
>> +            memcpy_fromio(match->rx_buf, mem->payload, len);
>> +        }
>>
>> -        match->status = le32_to_cpu(mem->status);
>> -        memcpy_fromio(match->rx_buf, mem->payload, len);
>>          if (match->rx_len > len)
>>              memset(match->rx_buf + len, 0, match->rx_len - len);
>> +
> 
> Spurious ?

Yep

> 
>>          complete(&match->done);
>>      }
>>      spin_unlock_irqrestore(&ch->rx_lock, flags);
>> @@ -331,7 +447,12 @@ static void scpi_handle_remote_msg(struct mbox_client *c, void *msg)
>>  {
>>      struct scpi_chan *ch = container_of(c, struct scpi_chan, cl);
>>      struct scpi_shared_mem *mem = ch->rx_payload;
>> -    u32 cmd = le32_to_cpu(mem->command);
>> +    u32 cmd;
>> +
>> +    if (scpi_info->is_legacy)
>> +        cmd = *(u32 *)msg;
> 
> Do we need do this if it doesn't contain command ?

No, will remove.

> 
>> +    else
>> +        cmd = le32_to_cpu(mem->command);
>>
>>      scpi_process_cmd(ch, cmd);
>>  }
>> @@ -343,17 +464,26 @@ static void scpi_tx_prepare(struct mbox_client *c, void *msg)
>>      struct scpi_chan *ch = container_of(c, struct scpi_chan, cl);
>>      struct scpi_shared_mem *mem = (struct scpi_shared_mem *)ch->tx_payload;
>>
>> -    if (t->tx_buf)
>> -        memcpy_toio(mem->payload, t->tx_buf, t->tx_len);
>> +    if (t->tx_buf) {
>> +        if (scpi_info->is_legacy)
>> +            memcpy_toio(ch->tx_payload, t->tx_buf, t->tx_len);
>> +        else
>> +            memcpy_toio(mem->payload, t->tx_buf, t->tx_len);
>> +    }
>> +
>>      if (t->rx_buf) {
>>          if (!(++ch->token))
>>              ++ch->token;
>>          ADD_SCPI_TOKEN(t->cmd, ch->token);
>> +        if (scpi_info->is_legacy)
>> +            t->slot = t->cmd;
> 
> I thought passing token was not an issue from your previous response,
> but you are overriding it here, why ?

Indeed, I can leave it, but it's useless since it won't serve to distinguish multiple similar commands.

> 
>>          spin_lock_irqsave(&ch->rx_lock, flags);
>>          list_add_tail(&t->node, &ch->rx_pending);
>>          spin_unlock_irqrestore(&ch->rx_lock, flags);
>>      }
>> -    mem->command = cpu_to_le32(t->cmd);
>> +
>> +    if (!scpi_info->is_legacy)
>> +        mem->command = cpu_to_le32(t->cmd);
>>  }
>>
>>  static struct scpi_xfer *get_scpi_xfer(struct scpi_chan *ch)
>> @@ -396,21 +526,37 @@ static int scpi_send_message(unsigned int offset, void *tx_buf,
>>
>>      cmd = scpi_info->scpi_cmds[offset];
>>
>> -    chan = atomic_inc_return(&scpi_info->next_chan) % scpi_info->num_chans;
>> +    if (scpi_info->is_legacy)
>> +        chan = test_bit(cmd, scpi_info->cmd_priority) ? 1 : 0;
>> +    else
>> +        chan = atomic_inc_return(&scpi_info->next_chan) %
>> +            scpi_info->num_chans;
>>      scpi_chan = scpi_info->channels + chan;
>>
>>      msg = get_scpi_xfer(scpi_chan);
>>      if (!msg)
>>          return -ENOMEM;
>>
>> -    msg->slot = BIT(SCPI_SLOT);
>> -    msg->cmd = PACK_SCPI_CMD(cmd, tx_len);
>> +    if (scpi_info->is_legacy) {
>> +        msg->cmd = PACK_LEGACY_SCPI_CMD(cmd, tx_len);
>> +        msg->slot = msg->cmd;
>> +    } else {
>> +        msg->slot = BIT(SCPI_SLOT);
>> +        msg->cmd = PACK_SCPI_CMD(cmd, tx_len);
>> +    }
>>      msg->tx_buf = tx_buf;
>>      msg->tx_len = tx_len;
>>      msg->rx_buf = rx_buf;
>>      msg->rx_len = rx_len;
>>      init_completion(&msg->done);
>>
>> +    /* Since we cannot distinguish the original command in the
>> +     * MHU reply stat value from a Legacy SCP firmware, ensure
>> +     * sequential command sending to the firmware.
>> +     */
> 
> OK this comment now questions the existence of this extra lock.
> The mailbox will always send the commands in the sequential order.
> It's only firmware that can re-order the response. Since that can't
> happen in you case, I really don't see the need for this.
> 
> Please explain the race you would see without this locking. Yes I
> understand that only one command is supposed to be sent to firmware at a
> time. Suppose you allow more callers here, all will wait on the
> completion flags and the first in the list gets unblocked right ?
> I am just trying to understand if there's real need for this extra
> lock when we already have that from the list.

In my current tests I have huge kernel hang when having multiple callers,
I must find out where this issue comes from...
In any case, we have an issue about the command sequencing.
If we push a tx-only command and then right after a tx-rx command, the
mailbox callback from the first command won't be able to distinguish which
command is handled !
In this case, the rx_pending list will not be empty, some garbage will be returned
to the second command handler and the real data from the second command handling
will be lost thinking it's a tx-only command.


We have two choices here :
 - Also push the tx-only commands to the rx_pending list, and also wait for their completion
 - Add an extra lock

What is your preferred scheme ?

>> +    if (scpi_info->is_legacy)
>> +        mutex_lock(&scpi_chan->legacy_lock);
>> +
>>      ret = mbox_send_message(scpi_chan->chan, msg);
>>      if (ret < 0 || !rx_buf)
>>          goto out;
>> @@ -421,9 +567,13 @@ static int scpi_send_message(unsigned int offset, void *tx_buf,
>>          /* first status word */
>>          ret = msg->status;
>>  out:
>> -    if (ret < 0 && rx_buf) /* remove entry from the list if timed-out */
>> +    if (ret < 0 && rx_buf)
>> +        /* remove entry from the list if timed-out */
>>          scpi_process_cmd(scpi_chan, msg->cmd);
>>
>> +    if (scpi_info->is_legacy)
>> +        mutex_unlock(&scpi_chan->legacy_lock);
>> +
>>      put_scpi_xfer(msg, scpi_chan);
>>      /* SCPI error codes > 0, translate them to Linux scale*/
>>      return ret > 0 ? scpi_to_linux_errno(ret) : ret;
> 
> [...]
> 
>> @@ -525,7 +687,6 @@ static struct scpi_dvfs_info *scpi_dvfs_get_info(u8 domain)
>>
>>      info->count = DVFS_OPP_COUNT(buf.header);
>>      info->latency = DVFS_LATENCY(buf.header) * 1000; /* uS to nS */
>> -
> 
> Spurious ?

Indeed.

> 
>>      info->opps = kcalloc(info->count, sizeof(*opp), GFP_KERNEL);
>>      if (!info->opps) {
>>          kfree(info);
>> @@ -580,9 +741,13 @@ static int scpi_sensor_get_value(u16 sensor, u64 *val)
>>
>>      ret = scpi_send_message(CMD_SENSOR_VALUE, &id, sizeof(id),
>>                  &buf, sizeof(buf));
>> -    if (!ret)
>> -        *val = (u64)le32_to_cpu(buf.hi_val) << 32 |
>> -            le32_to_cpu(buf.lo_val);
>> +    if (!ret) {
>> +        if (scpi_info->is_legacy)
>> +            *val = (u64)le32_to_cpu(buf.lo_val);
>> +        else
>> +            *val = (u64)le32_to_cpu(buf.hi_val) << 32 |
>> +                le32_to_cpu(buf.lo_val);
>> +    }
> 
> Not required as I have mentioned couple of times in previous versions,
> it's zero filled by the driver.
> 

OK

I will fix the issues, but I need your advice for the locking scheme. I really want this
to be merged and be able to go forward !

Thanks,
Neil

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