On Fri, Jan 08, 2021 at 01:59:13PM +0000, Peter Geis wrote:
> Currently hda on tegra30 fails to open a stream with an input/output error.
> 
> For example:
> speaker-test -Dhw:0,3 -c 2
> 
> speaker-test 1.2.2
> 
> Playback device is hw:0,3
> Stream parameters are 48000Hz, S16_LE, 2 channels
> Using 16 octaves of pink noise
> Rate set to 48000Hz (requested 48000Hz)
> Buffer size range from 64 to 16384
> Period size range from 32 to 8192
> Using max buffer size 16384
> Periods = 4
> was set period_size = 4096
> was set buffer_size = 16384
>  0 - Front Left
> Write error: -5,Input/output error
> xrun_recovery failed: -5,Input/output error
> Transfer failed: Input/output error
> 
> The tegra-hda device was introduced in tegra30 but only utilized in
> tegra124 until recent chips. Tegra210/186 work only due to a hardware
> change. For this reason it is unknown when this issue first manifested.
> Discussions with the hardware team show this applies to all current tegra
> chips. It has been resolved in the tegra234, which does not have hda
> support at this time.
> 
> The explanation from the hardware team is this:
> Below is the striping formula referenced from HD audio spec.
>    { ((num_channels * bits_per_sample) / number of SDOs) >= 8 }
> 
> The current issue is seen because Tegra HW has a problem with boundary
> condition (= 8) for striping. The reason why it is not seen on
> Tegra210/Tegra186 is because it uses max 2SDO lines. Max SDO lines is
> read from GCAP register.
> 
> For the given stream (channels = 2, bps = 16);
> ratio = (channels * bps) / NSDO = 32 / NSDO;
> 
> On Tegra30,      ratio = 32/4 = 8  (FAIL)
> On Tegra210/186, ratio = 32/2 = 16 (PASS)
> On Tegra194,     ratio = 32/4 = 8  (FAIL) ==> Earlier workaround was
> applied for it
> 
> If Tegra210/186 is forced to use 4SDO, it fails there as well. So the
> behavior is consistent across all these chips.
> 
> Applying the fix in [1] universally resolves this issue on tegra30-hda.
> Tested on the Ouya game console and the tf201 tablet.
> 
> [1] commit 60019d8c650d ("ALSA: hda/tegra: workaround playback failure on
> Tegra194")
> 
> Reviewed-by: Jon Hunter <jonathanh@nvidia.com>
> Tested-by: Ion Agorria <ion@agorria.com>
> Signed-off-by: Peter Geis <pgwipeout@gmail.com>
> ---
>  sound/pci/hda/hda_tegra.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/sound/pci/hda/hda_tegra.c b/sound/pci/hda/hda_tegra.c
> index 70164d1428d4..361cf2041911 100644
> --- a/sound/pci/hda/hda_tegra.c
> +++ b/sound/pci/hda/hda_tegra.c
> @@ -388,7 +388,7 @@ static int hda_tegra_first_init(struct azx *chip, struct platform_device *pdev)
>  	 * in powers of 2, next available ratio is 16 which can be
>  	 * used as a limiting factor here.
>  	 */
> -	if (of_device_is_compatible(np, "nvidia,tegra194-hda"))
> +	if (of_device_is_compatible(np, "nvidia,tegra30-hda"))
>  		chip->bus.core.sdo_limit = 16;

I think ideally this would be a SoC-specific property derived from the
compatible string, but since this preexisting:

Acked-by: Thierry Reding <treding@nvidia.com>