Re: [PATCH] drm/exynos: dsi: fix workaround for the legacy clock name

[Andrzej Hajda <a.hajda@samsung.com>]

On 20.02.2020 13:30, Marek Szyprowski wrote:
> Writing to the built-in strings arrays doesn't work if driver is loaded
> as kernel module. This is also considered as a bad pattern. Fix this by
> adding a call to clk_get() with legacy clock name. This fixes following
> kernel oops if driver is loaded as module:
>
> Unable to handle kernel paging request at virtual address bf047978
>  pgd = (ptrval)
>  [bf047978] *pgd=59344811, *pte=5903c6df, *ppte=5903c65f
>  Internal error: Oops: 80f [#1] SMP ARM
>  Modules linked in: mc exynosdrm(+) analogix_dp rtc_s3c exynos_ppmu i2c_gpio
>  CPU: 1 PID: 212 Comm: systemd-udevd Not tainted 5.6.0-rc2-next-20200219 #326
>  videodev: Linux video capture interface: v2.00
>  Hardware name: Samsung Exynos (Flattened Device Tree)
>  PC is at exynos_dsi_probe+0x1f0/0x384 [exynosdrm]
>  LR is at exynos_dsi_probe+0x1dc/0x384 [exynosdrm]
>  ...
>  Process systemd-udevd (pid: 212, stack limit = 0x(ptrval))
>  ...
>  [<bf03cf14>] (exynos_dsi_probe [exynosdrm]) from [<c09b1ca0>] (platform_drv_probe+0x6c/0xa4)
>  [<c09b1ca0>] (platform_drv_probe) from [<c09afcb8>] (really_probe+0x210/0x350)
>  [<c09afcb8>] (really_probe) from [<c09aff74>] (driver_probe_device+0x60/0x1a0)
>  [<c09aff74>] (driver_probe_device) from [<c09b0254>] (device_driver_attach+0x58/0x60)
>  [<c09b0254>] (device_driver_attach) from [<c09b02dc>] (__driver_attach+0x80/0xbc)
>  [<c09b02dc>] (__driver_attach) from [<c09ade00>] (bus_for_each_dev+0x68/0xb4)
>  [<c09ade00>] (bus_for_each_dev) from [<c09aefd8>] (bus_add_driver+0x130/0x1e8)
>  [<c09aefd8>] (bus_add_driver) from [<c09b0d64>] (driver_register+0x78/0x110)
>  [<c09b0d64>] (driver_register) from [<bf038558>] (exynos_drm_init+0xe8/0x11c [exynosdrm])
>  [<bf038558>] (exynos_drm_init [exynosdrm]) from [<c0302fa8>] (do_one_initcall+0x50/0x220)
>  [<c0302fa8>] (do_one_initcall) from [<c03dd02c>] (do_init_module+0x60/0x210)
>  [<c03dd02c>] (do_init_module) from [<c03dbf44>] (load_module+0x1c0c/0x2310)
>  [<c03dbf44>] (load_module) from [<c03dc85c>] (sys_finit_module+0xac/0xbc)
>  [<c03dc85c>] (sys_finit_module) from [<c0301000>] (ret_fast_syscall+0x0/0x54)
>  Exception stack(0xd979bfa8 to 0xd979bff0)
>  ...
>  ---[ end trace db16efe05faab470 ]---
>
> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>


Why did it worked with build-in driver remains mystery.


Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>

 --
Regards
Andrzej


> ---
>  drivers/gpu/drm/exynos/exynos_drm_dsi.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/exynos/exynos_drm_dsi.c b/drivers/gpu/drm/exynos/exynos_drm_dsi.c
> index 33628d85edad..08a8ce3f499c 100644
> --- a/drivers/gpu/drm/exynos/exynos_drm_dsi.c
> +++ b/drivers/gpu/drm/exynos/exynos_drm_dsi.c
> @@ -1787,9 +1787,10 @@ static int exynos_dsi_probe(struct platform_device *pdev)
>  		dsi->clks[i] = devm_clk_get(dev, clk_names[i]);
>  		if (IS_ERR(dsi->clks[i])) {
>  			if (strcmp(clk_names[i], "sclk_mipi") == 0) {
> -				strcpy(clk_names[i], OLD_SCLK_MIPI_CLK_NAME);
> -				i--;
> -				continue;
> +				dsi->clks[i] = devm_clk_get(dev,
> +							OLD_SCLK_MIPI_CLK_NAME);
> +				if (!IS_ERR(dsi->clks[i]))
> +					continue;
>  			}
>  
>  			dev_info(dev, "failed to get the clock: %s\n",


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