Re: [PATCH v2] mailbox: pcc: Support HW-Reduced Communication Subspace Type 2

[Hoan Tran <hotran@apm.com>]

Hi Alexey,

On Mon, May 9, 2016 at 2:43 AM, Alexey Klimov <alexey.klimov@arm.com> wrote:
> Hi Hoan,
>
> On Fri, May 06, 2016 at 11:38:34AM -0700, Hoan Tran wrote:
>> From: hotran <hotran@apm.com>
>>
>> ACPI 6.1 has a PCC HW-Reduced Communication Subspace Type 2 intended for
>> use on HW-Reduce ACPI Platform, which requires read-modify-write sequence
>> to acknowledge doorbell interrupt. This patch provides the implementation
>> for the Communication Subspace Type 2.
>>
>> This patch depends on patch [1] which supports PCC subspace type 2 header
>> [1] https://lkml.org/lkml/2016/5/5/14
>>  - [PATCH v2 03/13] ACPICA: ACPI 6.1: Support for new PCCT subtable
>
> So you finally decided to use separate structure declaration for type 2. Good.
>
>> v2
>>  * Remove changes inside "actbl3.h". This file is taken care by ACPICA.
>>  * Parse both subspace type 1 and subspace type 2
>>  * Remove unnecessary variable initialization
>>  * ISR returns IRQ_NONE in case of error
>>
>> v1
>>  * Initial
>>
>> Signed-off-by: Hoan Tran <hotran@apm.com>
>> ---
>>  drivers/mailbox/pcc.c | 395 +++++++++++++++++++++++++++++++++++++-------------
>>  1 file changed, 296 insertions(+), 99 deletions(-)
>>
>> diff --git a/drivers/mailbox/pcc.c b/drivers/mailbox/pcc.c
>> index 043828d..58c9a67 100644
>> --- a/drivers/mailbox/pcc.c
>> +++ b/drivers/mailbox/pcc.c
>> @@ -59,6 +59,7 @@
>>  #include <linux/delay.h>
>>  #include <linux/io.h>
>>  #include <linux/init.h>
>
> [...]
>
>> @@ -307,6 +440,43 @@ static int parse_pcc_subspace(struct acpi_subtable_header *header,
>>  }
>>
>>  /**
>> + * pcc_parse_subspace_irq - Parse the PCC IRQ and PCC ACK register
>> + *           There should be one entry per PCC client.
>> + * @mbox_chans: Pointer to the PCC mailbox channel data
>> + * @pcct_ss: Pointer to the ACPI subtable header under the PCCT.
>> + *
>> + * Return: 0 for Success, else errno.
>> + *
>> + * This gets called for each entry in the PCC table.
>> + */
>> +static int pcc_parse_subspace_irq(struct pcc_mbox_chan *mbox_chans,
>> +             struct acpi_pcct_hw_reduced *pcct_ss)
>> +{
>> +     mbox_chans->irq = pcc_map_interrupt(pcct_ss->doorbell_interrupt,
>> +                                         (u32)pcct_ss->flags);
>> +     if (mbox_chans->irq <= 0) {
>> +             pr_err("PCC GSI %d not registered\n",
>> +                    pcct_ss->doorbell_interrupt);
>> +             return -EINVAL;
>> +     }
>> +
>> +     if (pcct_ss->header.type
>> +             == ACPI_PCCT_TYPE_HW_REDUCED_SUBSPACE_TYPE2) {
>> +             struct acpi_pcct_hw_reduced_type2 *pcct2_ss = (void *)pcct_ss;
>> +
>> +             mbox_chans->pcc_doorbell_ack_vaddr = acpi_os_ioremap(
>> +                             pcct2_ss->doorbell_ack_register.address,
>> +                             pcct2_ss->doorbell_ack_register.bit_width / 8);
>> +             if (!mbox_chans->pcc_doorbell_ack_vaddr) {
>> +                     pr_err("Failed to ioremap PCC ACK register\n");
>> +                     return -ENOMEM;
>> +             }
>> +     }
>> +
>> +     return 0;
>> +}
>> +
>> +/**
>>   * acpi_pcc_probe - Parse the ACPI tree for the PCCT.
>>   *
>>   * Return: 0 for Success, else errno.
>> @@ -316,7 +486,8 @@ static int __init acpi_pcc_probe(void)
>>       acpi_size pcct_tbl_header_size;
>>       struct acpi_table_header *pcct_tbl;
>>       struct acpi_subtable_header *pcct_entry;
>> -     int count, i;
>> +     struct acpi_table_pcct *acpi_pcct_tbl;
>> +     int count, i, rc;
>>       acpi_status status = AE_OK;
>>
>>       /* Search for PCCT */
>> @@ -334,22 +505,28 @@ static int __init acpi_pcc_probe(void)
>>                       ACPI_PCCT_TYPE_HW_REDUCED_SUBSPACE,
>>                       parse_pcc_subspace, MAX_PCC_SUBSPACES);
>>
>> +     count += acpi_table_parse_entries(ACPI_SIG_PCCT,
>> +                     sizeof(struct acpi_table_pcct),
>> +                     ACPI_PCCT_TYPE_HW_REDUCED_SUBSPACE_TYPE2,
>> +                     parse_pcc_subspace, MAX_PCC_SUBSPACES);
>> +
>>       if (count <= 0) {
>>               pr_err("Error parsing PCC subspaces from PCCT\n");
>>               return -EINVAL;
>>       }
>
> Looks like after first call to acpi_table_parse_entries() you may have negative
> number in count. And then you add counted number of type 2 subtables to count variable.
>
> I am not aware how pedantic this all should be but you may have more than MAX_PCC_SUBSPACES
> subspaces or don't probe any subspaces at all with such approach. Or other side effects.
I should check the "count" at first call acpi_table_parse_entries().
If "count < 0", assign count=0, then call the next
acpi_table_parse_entries().

Thanks for your review
-Hoan
>
>
> Best regards,
> Alexey Klimov

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