Re: [PATCH 2/2] ASoC: fsl_ssi: Add monaural audio support for non-ac97 interface

On Fri, Nov 15, 2013 at 12:21:08PM +0000, Russell King - ARM Linux wrote:

quoted

@@ -517,10 +517,12 @@ static int fsl_ssi_hw_params(struct snd_pcm_substream *substream,
 {
 	struct fsl_ssi_private *ssi_private = snd_soc_dai_get_drvdata(cpu_dai);
 	struct ccsr_ssi __iomem *ssi = ssi_private->ssi;
+	unsigned int channels = params_channels(hw_params);
 	unsigned int sample_size =
 		snd_pcm_format_width(params_format(hw_params));
 	u32 wl = CCSR_SSI_SxCCR_WL(sample_size);
 	int enabled = read_ssi(&ssi->scr) & CCSR_SSI_SCR_SSIEN;
+	static u8 i2s_mode;

Throwing a static variable into the middle of a driver with none is a
really horrid thing to do and is very bad programming practice.  What
if some freescale device decides to have to of these interfaces?  Both
will try to use this same static variable.

This is extremely bad programming practice.

Sir, I'm glad you're teaching me this lesson. I did hesitate before I
sent this patch, just couldn't tell the reason. And swear to god, I
hadn't used and will never use this practice again.
 

quoted

+	/* Save i2s mode configuration so that we can restore it later */
+	switch (read_ssi(&ssi->scr) & CCSR_SSI_SCR_I2S_MODE_MASK) {
+	case CCSR_SSI_SCR_I2S_MODE_SLAVE:
+	case CCSR_SSI_SCR_I2S_MODE_MASTER:
+		i2s_mode = read_ssi(&ssi->scr) & CCSR_SSI_SCR_I2S_MODE_MASK;
+	default:
+		break;
+	}

So all you're doing is saving the mode only if it specifies master or
slave mode, but not if it's normal mode (== 0).  This just looks like
it's complicated just for the sake of being complicated.

Since we know what mode this is in when we run fsl_ssi_setup(), can we
not save that value into the fsl_ssi_private structure and re-use it
here?

Currently we only have fsl_ssi_setup() to set I2S mode. It's definitely
a good idea to save it into private structure at that point. But there
will be new ASoC function -- set_dai_fmt() appending to this driver.
It will provide ASoC machine driver an interface to set I2S mode again,
and we must put a saving code as well at that time. So I think put the
saving code here would keep the modification within a small range. But
I here might be so obsessed with trying to make the patch as neat as
possible that I picked a demon sword.

But I'm still willing to learn the lesson. And I'll refine this patch.

Much obliged,
Nicolin Chen