net: stmmac: stmmac_platform: fix parsing of DT binding

commit 64c3b252 ("net: stmmac: fixed the pbl setting with DT")
changed the parsing of the DT binding.

Before 64c3b252, snps,fixed-burst and snps,mixed-burst were parsed
regardless if the property snps,pbl existed or not.
After the commit, fixed burst and mixed burst are only parsed if
snps,pbl exists. Now when snps,aal has been added, it too is only
parsed if snps,pbl exists.

Since the DT binding does not specify that fixed burst, mixed burst
or aal depend on snps,pbl being specified, undo changes introduced
by 64c3b252.

The issue commit 64c3b252 ("net: stmmac: fixed the pbl setting with
DT") tries to address is solved in another way:
The databook specifies that all values other than
1, 2, 4, 8, 16, or 32 results in undefined behavior,
so snps,pbl = <0> is invalid.

If pbl is 0 after parsing, set pbl to DEFAULT_DMA_PBL.
This handles the case where the property is omitted, and also handles
the case where the property is specified without any data.
Signed-off-by: Niklas Cassel <niklas.cassel@axis.com>
Acked-by: Alexandre Torgue <alexandre.torgue@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/stmmac_main.c

@@ -1581,8 +1581,8 @@ static int stmmac_init_dma_engine(struct stmmac_priv *priv)
 	int atds = 0;
 	int ret = 0;
 
-	if (!priv->plat->dma_cfg) {
-		dev_err(priv->device, "DMA configuration not found\n");
+	if (!priv->plat->dma_cfg || !priv->plat->dma_cfg->pbl) {
+		dev_err(priv->device, "Invalid DMA configuration\n");
 		return -EINVAL;
 	}
 

drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c

@@ -304,7 +304,6 @@ stmmac_probe_config_dt(struct platform_device *pdev, const char **mac)
 		plat->force_sf_dma_mode = 1;
 	}
 
-	if (of_find_property(np, "snps,pbl", NULL)) {
 	dma_cfg = devm_kzalloc(&pdev->dev, sizeof(*dma_cfg),
 			       GFP_KERNEL);
 	if (!dma_cfg) {
@@ -312,13 +311,15 @@ stmmac_probe_config_dt(struct platform_device *pdev, const char **mac)
 		return ERR_PTR(-ENOMEM);
 	}
 	plat->dma_cfg = dma_cfg;
+
 	of_property_read_u32(np, "snps,pbl", &dma_cfg->pbl);
+	if (!dma_cfg->pbl)
+		dma_cfg->pbl = DEFAULT_DMA_PBL;
+
 	dma_cfg->aal = of_property_read_bool(np, "snps,aal");
-		dma_cfg->fixed_burst =
-			of_property_read_bool(np, "snps,fixed-burst");
-		dma_cfg->mixed_burst =
-			of_property_read_bool(np, "snps,mixed-burst");
-	}
+	dma_cfg->fixed_burst = of_property_read_bool(np, "snps,fixed-burst");
+	dma_cfg->mixed_burst = of_property_read_bool(np, "snps,mixed-burst");
+
 	plat->force_thresh_dma_mode = of_property_read_bool(np, "snps,force_thresh_dma_mode");
 	if (plat->force_thresh_dma_mode) {
 		plat->force_sf_dma_mode = 0;