Re: [PATCH] ASoC: AMD: Fix race condition between register access

["Agrawal, Akshu" <Akshu.Agrawal@amd.com>]

On 10/30/2018 7:02 AM, Daniel Kurtz wrote:
> Hi Akshu,
> 
> 
> On Mon, Oct 29, 2018 at 1:39 AM Agrawal, Akshu <Akshu.Agrawal@amd.com> wrote:
>>
>> During simultaneous running of playback and capture, we
>> got hit by incorrect value write on common register. This was due
>> to race condition between 2 streams.
>> Fixing this by locking the common register access.
> 
> Nice catch!  It looks looks like one of the operations you are trying
> to make atomic is that two step Addr + Data register update.
> If so, then I recommend refactoring a bit, and just doing that locked
> 2-step-access in its own helper function, like this:
> 
>   static void acp_reg_write_srbm_targ(void __iomem *acp_mmio, u32
> addr, u32 data)
>   {
>     unsigned long flags;
> 
>     spin_lock_irqsave(&lock, flags);
>     acp_reg_write(addr, acp_mmio, mmACP_SRBM_Targ_Idx_Addr);
>     acp_reg_write(data, acp_mmio, mmACP_SRBM_Targ_Idx_Data);
>     spin_unlock_irqrestore(&lock, flags);
>   }
> 
> And similarly, you can add 2 more locking helpers, one for modifying
> the imr/ch and another for mmACP_I2S_16BIT_RESOLUTION_EN.
> 

Accepted, will add the helper functions and push another patch.
Also, I noticed that locking is not needed in imr and ch reg as these
are separate registers for each channel, so will remove that.

Thanks,
Akshu
>>
>> Signed-off-by: Akshu Agrawal <akshu.agrawal@amd.com>
>> ---
>>  sound/soc/amd/acp-pcm-dma.c | 29 +++++++++++++++++++++++++++++
>>  1 file changed, 29 insertions(+)
>>
>> diff --git a/sound/soc/amd/acp-pcm-dma.c b/sound/soc/amd/acp-pcm-dma.c
>> index 0ac4b5b..993a7db 100644
>> --- a/sound/soc/amd/acp-pcm-dma.c
>> +++ b/sound/soc/amd/acp-pcm-dma.c
>> @@ -121,6 +121,9 @@
>>         .periods_max = CAPTURE_MAX_NUM_PERIODS,
>>  };
>>
>> +/* Lock to protect access to registers */
>> +static DEFINE_SPINLOCK(lock);
>> +
>>  static u32 acp_reg_read(void __iomem *acp_mmio, u32 reg)
>>  {
>>         return readl(acp_mmio + (reg * 4));
>> @@ -168,9 +171,12 @@ static void config_dma_descriptor_in_sram(void __iomem *acp_mmio,
>>                                           acp_dma_dscr_transfer_t *descr_info)
>>  {
>>         u32 sram_offset;
>> +       unsigned long flags;
>>
>>         sram_offset = (descr_idx * sizeof(acp_dma_dscr_transfer_t));
>>
>> +       spin_lock_irqsave(&lock, flags);
>> +
>>         /* program the source base address. */
>>         acp_reg_write(sram_offset, acp_mmio, mmACP_SRBM_Targ_Idx_Addr);
>>         acp_reg_write(descr_info->src,  acp_mmio, mmACP_SRBM_Targ_Idx_Data);
>> @@ -181,6 +187,8 @@ static void config_dma_descriptor_in_sram(void __iomem *acp_mmio,
>>         /* program the number of bytes to be transferred for this descriptor. */
>>         acp_reg_write(sram_offset + 8,  acp_mmio, mmACP_SRBM_Targ_Idx_Addr);
>>         acp_reg_write(descr_info->xfer_val, acp_mmio, mmACP_SRBM_Targ_Idx_Data);
>> +
>> +       spin_unlock_irqrestore(&lock, flags);
>>  }
>>
>>  static void pre_config_reset(void __iomem *acp_mmio, u16 ch_num)
>> @@ -309,8 +317,12 @@ static void acp_pte_config(void __iomem *acp_mmio, struct page *pg,
>>         u32 low;
>>         u32 high;
>>         u32 offset;
>> +       unsigned long flags;
>>
>>         offset  = ACP_DAGB_GRP_SRBM_SRAM_BASE_OFFSET + (pte_offset * 8);
>> +
>> +       spin_lock_irqsave(&lock, flags);
>> +
>>         for (page_idx = 0; page_idx < (num_of_pages); page_idx++) {
>>                 /* Load the low address of page int ACP SRAM through SRBM */
>>                 acp_reg_write((offset + (page_idx * 8)),
>> @@ -333,6 +345,8 @@ static void acp_pte_config(void __iomem *acp_mmio, struct page *pg,
>>                 /* Move to next physically contiguos page */
>>                 pg++;
>>         }
>> +
>> +       spin_unlock_irqrestore(&lock, flags);
>>  }
>>
>>  static void config_acp_dma(void __iomem *acp_mmio,
>> @@ -367,6 +381,7 @@ static void acp_dma_cap_channel_enable(void __iomem *acp_mmio,
>>                                        u16 cap_channel)
>>  {
>>         u32 val, ch_reg, imr_reg, res_reg;
>> +       unsigned long flags;
>>
>>         switch (cap_channel) {
>>         case CAP_CHANNEL1:
>> @@ -381,6 +396,8 @@ static void acp_dma_cap_channel_enable(void __iomem *acp_mmio,
>>                 imr_reg = mmACP_I2SMICSP_IMR0;
>>                 break;
>>         }
>> +       spin_lock_irqsave(&lock, flags);
>> +
>>         val = acp_reg_read(acp_mmio,
>>                            mmACP_I2S_16BIT_RESOLUTION_EN);
>>         if (val & ACP_I2S_MIC_16BIT_RESOLUTION_EN) {
>> @@ -393,12 +410,15 @@ static void acp_dma_cap_channel_enable(void __iomem *acp_mmio,
>>         val &= ~ACP_I2SMICSP_IMR1__I2SMICSP_RXFOM_MASK;
>>         acp_reg_write(val, acp_mmio, imr_reg);
>>         acp_reg_write(0x1, acp_mmio, ch_reg);
>> +
>> +       spin_unlock_irqrestore(&lock, flags);
>>  }
>>
>>  static void acp_dma_cap_channel_disable(void __iomem *acp_mmio,
>>                                         u16 cap_channel)
>>  {
>>         u32 val, ch_reg, imr_reg;
>> +       unsigned long flags;
>>
>>         switch (cap_channel) {
>>         case CAP_CHANNEL1:
>> @@ -411,11 +431,15 @@ static void acp_dma_cap_channel_disable(void __iomem *acp_mmio,
>>                 ch_reg = mmACP_I2SMICSP_RER0;
>>                 break;
>>         }
>> +       spin_lock_irqsave(&lock, flags);
>> +
>>         val = acp_reg_read(acp_mmio, imr_reg);
>>         val |= ACP_I2SMICSP_IMR1__I2SMICSP_RXDAM_MASK;
>>         val |= ACP_I2SMICSP_IMR1__I2SMICSP_RXFOM_MASK;
>>         acp_reg_write(val, acp_mmio, imr_reg);
>>         acp_reg_write(0x0, acp_mmio, ch_reg);
>> +
>> +       spin_unlock_irqrestore(&lock, flags);
>>  }
>>
>>  /* Start a given DMA channel transfer */
>> @@ -847,6 +871,7 @@ static int acp_dma_hw_params(struct snd_pcm_substream *substream,
>>         int status;
>>         uint64_t size;
>>         u32 val = 0;
>> +       unsigned long flags;
>>         struct page *pg;
>>         struct snd_pcm_runtime *runtime;
>>         struct audio_substream_data *rtd;
>> @@ -870,6 +895,8 @@ static int acp_dma_hw_params(struct snd_pcm_substream *substream,
>>                 }
>>         }
>>         if (adata->asic_type == CHIP_STONEY) {
>> +               spin_lock_irqsave(&lock, flags);
>> +
>>                 val = acp_reg_read(adata->acp_mmio,
>>                                    mmACP_I2S_16BIT_RESOLUTION_EN);
>>                 if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) {
>> @@ -893,6 +920,8 @@ static int acp_dma_hw_params(struct snd_pcm_substream *substream,
>>                 }
>>                 acp_reg_write(val, adata->acp_mmio,
>>                               mmACP_I2S_16BIT_RESOLUTION_EN);
>> +
>> +               spin_unlock_irqrestore(&lock, flags);
>>         }
>>
>>         if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) {
>> --
>> 1.9.1
>>