[bug report] net: stmmac: fix dma physical address of descriptor when display ring

[Dan Carpenter <error27@gmail.com>]

Hello Joakim Zhang,

Commit bfaf91ca848e ("net: stmmac: fix dma physical address of
descriptor when display ring") from Feb 25, 2021 (linux-next), leads
to the following Smatch static checker warning:

	drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c:431 dwmac4_display_ring()
	warn: duplicate check 'desc_size == 32' (previous on line 418)

drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c
    399 static void dwmac4_display_ring(void *head, unsigned int size, bool rx,
    400                                 dma_addr_t dma_rx_phy, unsigned int desc_size)
    401 {
    402         dma_addr_t dma_addr;
    403         int i;
    404 
    405         pr_info("%s descriptor ring:\n", rx ? "RX" : "TX");
    406 
    407         if (desc_size == sizeof(struct dma_desc)) {
    408                 struct dma_desc *p = (struct dma_desc *)head;
    409 
    410                 for (i = 0; i < size; i++) {
    411                         dma_addr = dma_rx_phy + i * sizeof(*p);
    412                         pr_info("%03d [%pad]: 0x%x 0x%x 0x%x 0x%x\n",
    413                                 i, &dma_addr,
    414                                 le32_to_cpu(p->des0), le32_to_cpu(p->des1),
    415                                 le32_to_cpu(p->des2), le32_to_cpu(p->des3));
    416                         p++;
    417                 }
    418         } else if (desc_size == sizeof(struct dma_extended_desc)) {
    419                 struct dma_extended_desc *extp = (struct dma_extended_desc *)head;
    420 
    421                 for (i = 0; i < size; i++) {
    422                         dma_addr = dma_rx_phy + i * sizeof(*extp);
    423                         pr_info("%03d [%pad]: 0x%x 0x%x 0x%x 0x%x 0x%x 0x%x 0x%x 0x%x\n",
    424                                 i, &dma_addr,
    425                                 le32_to_cpu(extp->basic.des0), le32_to_cpu(extp->basic.des1),
    426                                 le32_to_cpu(extp->basic.des2), le32_to_cpu(extp->basic.des3),
    427                                 le32_to_cpu(extp->des4), le32_to_cpu(extp->des5),
    428                                 le32_to_cpu(extp->des6), le32_to_cpu(extp->des7));
    429                         extp++;
    430                 }
--> 431         } else if (desc_size == sizeof(struct dma_edesc)) {

The dma_extended_desc and dma_edesc structs are the same size but
just the basic info is at the start vs at the end.  This code is
quite old, but I think maybe we changed the Kconfig so now it's showing
up as a static checker warning?

/* Extended descriptor structure (e.g. >= databook 3.50a) */
struct dma_extended_desc {
	struct dma_desc basic;	/* Basic descriptors */
	__le32 des4;	/* Extended Status */
	__le32 des5;	/* Reserved */
	__le32 des6;	/* Tx/Rx Timestamp Low */
	__le32 des7;	/* Tx/Rx Timestamp High */
};

/* Enhanced descriptor for TBS */
struct dma_edesc {
	__le32 des4;
	__le32 des5;
	__le32 des6;
	__le32 des7;
	struct dma_desc basic;
};

    432                 struct dma_edesc *ep = dma_desc_to_edesc(head);
    433 
    434                 for (i = 0; i < size; i++) {
    435                         dma_addr = dma_rx_phy + i * sizeof(*ep);
    436                         pr_info("%03d [%pad]: 0x%x 0x%x 0x%x 0x%x 0x%x 0x%x 0x%x 0x%x\n",
    437                                 i, &dma_addr,
    438                                 le32_to_cpu(ep->des4), le32_to_cpu(ep->des5),
    439                                 le32_to_cpu(ep->des6), le32_to_cpu(ep->des7),
    440                                 le32_to_cpu(ep->basic.des0), le32_to_cpu(ep->basic.des1),
    441                                 le32_to_cpu(ep->basic.des2), le32_to_cpu(ep->basic.des3));
    442                         ep++;
    443                 }
    444         } else {
    445                 pr_err("unsupported descriptor!");
    446         }
    447 }

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regards,
dan carpenter