linux-kernel - Re: [PATCH 06/17] coresight: tmc: Make ETR SG table circular

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Date:   Thu, 2 Nov 2017 08:40:16 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Suzuki K Poulose <Suzuki.Poulose@....com>
Cc:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        rob.walker@....com, Mike Leach <mike.leach@...aro.org>,
        coresight@...ts.linaro.org
Subject: Re: [PATCH 06/17] coresight: tmc: Make ETR SG table circular

On 2 November 2017 at 06:00, Suzuki K Poulose <Suzuki.Poulose@....com> wrote:
> On 01/11/17 23:47, Mathieu Poirier wrote:
>>
>> On Thu, Oct 19, 2017 at 06:15:42PM +0100, Suzuki K Poulose wrote:
>>>
>>> Make the ETR SG table Circular buffer so that we could start
>>> at any of the SG pages and use the entire buffer for tracing.
>>> This can be achieved by :
>>>
>>> 1) Keeping an additional LINK pointer at the very end of the
>>> SG table, i.e, after the LAST buffer entry, to point back to
>>> the beginning of the first table. This will allow us to use
>>> the buffer normally when we start the trace at offset 0 of
>>> the buffer, as the LAST buffer entry hints the TMC-ETR and
>>> it automatically wraps to the offset 0.
>>>
>>> 2) If we want to start at any other ETR SG page aligned offset,
>>> we could :
>>>   a) Make the preceding page entry as LAST entry.
>>>   b) Make the original LAST entry a normal entry.
>>>   c) Use the table pointer to the "new" start offset as the
>>>      base of the table address.
>>> This works as the TMC doesn't mandate that the page table
>>> base address should be 4K page aligned.
>>>
>>> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
>>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
>>> ---
>
>
>>> +static int __maybe_unused
>>> +tmc_etr_sg_table_rotate(struct etr_sg_table *etr_table, u64 base_offset)
>>> +{
>>> +       u32 last_entry, first_entry;
>>> +       u64 last_offset;
>>> +       struct tmc_sg_table *sg_table = etr_table->sg_table;
>>> +       sgte_t *table_ptr = sg_table->table_vaddr;
>>> +       ssize_t buf_size = tmc_sg_table_buf_size(sg_table);
>>> +
>>> +       /* Offset should always be SG PAGE_SIZE aligned */
>>> +       if (base_offset & (ETR_SG_PAGE_SIZE - 1)) {
>>> +               pr_debug("unaligned base offset %llx\n", base_offset);
>>> +               return -EINVAL;
>>> +       }
>>> +       /* Make sure the offset is within the range */
>>> +       if (base_offset < 0 || base_offset > buf_size) {
>>> +               base_offset = (base_offset + buf_size) % buf_size;
>>> +               pr_debug("Resetting offset to %llx\n", base_offset);
>>> +       }
>>> +       first_entry = tmc_etr_sg_offset_to_table_index(base_offset);
>>> +       if (first_entry == etr_table->first_entry) {
>>> +               pr_debug("Head is already at %llx, skipping\n",
>>> base_offset);
>>> +               return 0;
>>> +       }
>>> +
>>> +       /* Last entry should be the previous one to the new "base" */
>>> +       last_offset = ((base_offset - ETR_SG_PAGE_SIZE) + buf_size) %
>>> buf_size;
>>> +       last_entry = tmc_etr_sg_offset_to_table_index(last_offset);
>>> +
>>> +       /* Reset the current Last page to Normal and new Last page to
>>> NORMAL */
>>> +       tmc_etr_sg_update_type(&table_ptr[etr_table->last_entry],
>>> +                                ETR_SG_ET_NORMAL);
>>> +       tmc_etr_sg_update_type(&table_ptr[last_entry], ETR_SG_ET_LAST);
>>> +       etr_table->hwaddr = tmc_etr_sg_table_index_to_daddr(sg_table,
>>> +                                                           first_entry);
>>> +       etr_table->first_entry = first_entry;
>>> +       etr_table->last_entry = last_entry;
>>> +       pr_debug("table rotated to offset %llx-%llx, entries (%d - %d),
>>> dba: %llx\n",
>>> +                       base_offset, last_offset, first_entry,
>>> last_entry,
>>> +                       etr_table->hwaddr);
>>
>>
>> The above line generates a warning when compiling for ARMv7.
>
>
> Where you running with LPAE off ? That could probably be the case,
> where hwaddr could be 32bit or 64bit depending on whether LPAE
> is enabled. I will fix it.

My original setup did not have LPAE configured but even when I do
configure it I can generate the warnings.

Compiler:

arm-linux-gnueabi-gcc (Ubuntu/Linaro 5.4.0-6ubuntu1~16.04.4) 5.4.0 20160609

Let me know if you want my .config file.

>
> I have fixed some other warnings with ARMv7 with LPAE.
>
> Suzuki