net: stmmac: Fix kernel panic due to NULL pointer dereference of fpe_cfg

net: stmmac: Fix kernel panic due to NULL pointer dereference of fpe_cfg

In this patch, "net: stmmac: support FPE link partner hand-shaking
procedure", priv->plat->fpe_cfg wouldn`t be "devm_kzalloc"ed if
dma_cap->frpsel is 0 (Flexible Rx Parser is not supported in SoC) in
tc_init(). So, fpe_cfg will be remain as NULL and accessing it will cause
kernel panic.

To fix this, move the "devm_kzalloc"ing of priv->plat->fpe_cfg before
dma_cap->frpsel checking in tc_init(). Additionally, checking of
priv->dma_cap.fpesel is added before calling stmmac_fpe_link_state_handle()
as only FPE supported SoC is allowed to call the function.

Below is the kernel panic dump reported by Marek Szyprowski
<m.szyprowski@samsung.com>:

meson8b-dwmac ff3f0000.ethernet eth0: PHY [0.0:00] driver [RTL8211F Gigabit Ethernet] (irq=35)
meson8b-dwmac ff3f0000.ethernet eth0: No Safety Features support found
meson8b-dwmac ff3f0000.ethernet eth0: PTP not supported by HW
meson8b-dwmac ff3f0000.ethernet eth0: configuring for phy/rgmii link mode
Unable to handle kernel NULL pointer dereference at virtual address 0000000000000001
Mem abort info:
...
user pgtable: 4k pages, 48-bit VAs, pgdp=00000000044eb000
[0000000000000001] pgd=0000000000000000, p4d=0000000000000000
Internal error: Oops: 96000004 [#1] PREEMPT SMP
Modules linked in: dw_hdmi_i2s_audio dw_hdmi_cec meson_gxl realtek meson_gxbb_wdt snd_soc_meson_axg_sound_card dwmac_generic axg_audio meson_dw_hdmi crct10dif_ce snd_soc_meson_card_utils snd_soc_meson_axg_tdmout panfrost rc_odroid gpu_sched reset_meson_audio_arb meson_ir snd_soc_meson_g12a_tohdmitx snd_soc_meson_axg_frddr sclk_div clk_phase snd_soc_meson_codec_glue dwmac_meson8b snd_soc_meson_axg_fifo stmmac_platform meson_rng meson_drm stmmac rtc_meson_vrtc rng_core meson_canvas pwm_meson dw_hdmi mdio_mux_meson_g12a pcs_xpcs snd_soc_meson_axg_tdm_interface snd_soc_meson_axg_tdm_formatter nvmem_meson_efuse display_connector
CPU: 1 PID: 7 Comm: kworker/u8:0 Not tainted 5.12.0-rc4-next-20210325+
Hardware name: Hardkernel ODROID-C4 (DT)
Workqueue: events_power_efficient phylink_resolve
pstate: 20400009 (nzCv daif +PAN -UAO -TCO BTYPE=--)
pc : stmmac_mac_link_up+0x14c/0x348 [stmmac]
lr : stmmac_mac_link_up+0x284/0x348 [stmmac] ...
Call trace:
 stmmac_mac_link_up+0x14c/0x348 [stmmac]
 phylink_resolve+0x104/0x420
 process_one_work+0x2a8/0x718
 worker_thread+0x48/0x460
 kthread+0x134/0x160
 ret_from_fork+0x10/0x18
Code: b971ba60 350007c0 f958c260 f9402000 (39400401)
---[ end trace 0c9deb6c510228aa ]---

Fixes: 5a5586112b92 ("net: stmmac: support FPE link partner hand-shaking
procedure")
Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Mohammad Athari Bin Ismail <mohammad.athari.ismail@intel.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: David S. Miller <davem@davemloft.net>