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Subject: Re: Onboard SD card doesn't work anymore after the 'mmc-v5.4-2'
 updates
From: Christian Zigotzky <chzigotzky@xenosoft.de>
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Date: Wed, 23 Oct 2019 16:20:42 +0200
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To: Michael Ellerman <mpe@ellerman.id.au>
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Cc: ulf.hansson@linaro.org, mad skateman <madskateman@gmail.com>,
 linux-mmc@vger.kernel.org,
 Russell King - ARM Linux admin <linux@armlinux.org.uk>,
 Rob Herring <robh+dt@kernel.org>, Paul Mackerras <paulus@samba.org>,
 "R.T.Dickinson" <rtd2@xtra.co.nz>, "contact@a-eon.com" <contact@a-eon.com>,
 linuxppc-dev@lists.ozlabs.org, Christian Zigotzky <info@xenosoft.de>
Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org
Sender: "Linuxppc-dev"
 <linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org>

Hello,

The patch below works. I compiled the RC4 of kernel 5.4 with this patch toda=
y and the onboard SD card works without any problems.

Thanks!

Christian

> On 23. Oct 2019, at 07:42, Michael Ellerman <mpe@ellerman.id.au> wrote:
>=20
> Russell King - ARM Linux admin <linux@armlinux.org.uk> writes:
>>> On Tue, Oct 15, 2019 at 03:12:49PM +0200, Christian Zigotzky wrote:
>>> Hello Russell,
>>>=20
>>> You asked me about "dma-coherent" in the Cyrus device tree. Unfortunatel=
y I
>>> don't find the property "dma-coherent" in the dtb source files.
>>>=20
>>> Output of "fdtdump cyrus_p5020_eth_poweroff.dtb | grep dma":
>>>=20
>>> dma0 =3D "/soc@ffe000000/dma@100300";
>>>         dma1 =3D "/soc@ffe000000/dma@101300";
>>>         dma@100300 {
>>>             compatible =3D "fsl,eloplus-dma";
>>>             dma-channel@0 {
>>>                 compatible =3D "fsl,eloplus-dma-channel";
>>>             dma-channel@80 {
>>>                 compatible =3D "fsl,eloplus-dma-channel";
>>>             dma-channel@100 {
>>>                 compatible =3D "fsl,eloplus-dma-channel";
>>>             dma-channel@180 {
>>>                 compatible =3D "fsl,eloplus-dma-channel";
>>>         dma@101300 {
>>>             compatible =3D "fsl,eloplus-dma";
>>>             dma-channel@0 {
>>>                 compatible =3D "fsl,eloplus-dma-channel";
>>>             dma-channel@80 {
>>>                 compatible =3D "fsl,eloplus-dma-channel";
>>>             dma-channel@100 {
>>>                 compatible =3D "fsl,eloplus-dma-channel";
>>>             dma-channel@180 {
>>>                 compatible =3D "fsl,eloplus-dma-channel";
>>=20
>> Hmm, so it looks like PowerPC doesn't mark devices that are dma
>> coherent with a property that describes them as such.
>>=20
>> I think this opens a wider question - what should of_dma_is_coherent()
>> return for PowerPC?  It seems right now that it returns false for
>> devices that are DMA coherent, which seems to me to be a recipe for
>> future mistakes.
>=20
> Right, it seems of_dma_is_coherent() has baked in the assumption that
> devices are non-coherent unless explicitly marked as coherent.
>=20
> Which is wrong on all or at least most existing powerpc systems
> according to Ben.
>=20
>> Any ideas from the PPC maintainers?
>=20
> Fixing it at the source seems like the best option to prevent future
> breakage.
>=20
> So I guess that would mean making of_dma_is_coherent() return true/false
> based on CONFIG_NOT_COHERENT_CACHE on powerpc.
>=20
> We could do it like below, which would still allow the dma-coherent
> property to work if it ever makes sense on a future powerpc platform.
>=20
> I don't really know any of this embedded stuff well, so happy to take
> other suggestions on how to handle this mess.
>=20
> cheers
>=20
>=20
> diff --git a/arch/powerpc/kernel/setup-common.c b/arch/powerpc/kernel/setu=
p-common.c
> index 25aaa3903000..b96c9010acb6 100644
> --- a/arch/powerpc/kernel/setup-common.c
> +++ b/arch/powerpc/kernel/setup-common.c
> @@ -760,6 +760,22 @@ static int __init check_cache_coherency(void)
> late_initcall(check_cache_coherency);
> #endif /* CONFIG_CHECK_CACHE_COHERENCY */
>=20
> +#ifndef CONFIG_NOT_COHERENT_CACHE
> +/*
> + * For historical reasons powerpc kernels are built with hard wired knowl=
edge of
> + * whether or not DMA accesses are cache coherent. Additionally device tr=
ees on
> + * powerpc do not typically support the dma-coherent property.
> + *
> + * So when we know that DMA is coherent, override arch_of_dma_is_coherent=
() to
> + * tell the drivers/of code that all devices are coherent regardless of w=
hether
> + * they have a dma-coherent property.
> + */
> +bool arch_of_dma_is_coherent(struct device_node *np)
> +{
> +    return true;
> +}
> +#endif
> +
> #ifdef CONFIG_DEBUG_FS
> struct dentry *powerpc_debugfs_root;
> EXPORT_SYMBOL(powerpc_debugfs_root);
> diff --git a/drivers/of/address.c b/drivers/of/address.c
> index 978427a9d5e6..3a4b2949a322 100644
> --- a/drivers/of/address.c
> +++ b/drivers/of/address.c
> @@ -993,6 +993,14 @@ int of_dma_get_range(struct device_node *np, u64 *dma=
_addr, u64 *paddr, u64 *siz
> }
> EXPORT_SYMBOL_GPL(of_dma_get_range);
>=20
> +/*
> + * arch_of_dma_is_coherent - Arch hook to determine if device is coherent=
 for DMA
> + */
> +bool __weak arch_of_dma_is_coherent(struct device_node *np)
> +{
> +    return false;
> +}
> +
> /**
>  * of_dma_is_coherent - Check if device is coherent
>  * @np:    device node
> @@ -1002,8 +1010,12 @@ EXPORT_SYMBOL_GPL(of_dma_get_range);
>  */
> bool of_dma_is_coherent(struct device_node *np)
> {
> -    struct device_node *node =3D of_node_get(np);
> +    struct device_node *node;
> +
> +    if (arch_of_dma_is_coherent(np))
> +        return true;
>=20
> +    np =3D of_node_get(np);
>    while (node) {
>        if (of_property_read_bool(node, "dma-coherent")) {
>            of_node_put(node);