Implement nvmem-provider functionality in mtk-mfg-pmdomain, such that it
can expose its GF_REG_SHADER_PRESENT value in the shared memory as an
nvmem cell for panthor.

Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
---
 drivers/pmdomain/mediatek/mtk-mfg-pmdomain.c | 57 ++++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)

diff --git a/drivers/pmdomain/mediatek/mtk-mfg-pmdomain.c b/drivers/pmdomain/mediatek/mtk-mfg-pmdomain.c
index 9bad577b3ae4..725ebc678f1b 100644
--- a/drivers/pmdomain/mediatek/mtk-mfg-pmdomain.c
+++ b/drivers/pmdomain/mediatek/mtk-mfg-pmdomain.c
@@ -10,6 +10,7 @@
 #include <linux/clk-provider.h>
 #include <linux/container_of.h>
 #include <linux/iopoll.h>
+#include <linux/nvmem-provider.h>
 #include <linux/mailbox_client.h>
 #include <linux/module.h>
 #include <linux/of.h>
@@ -872,6 +873,58 @@ static int mtk_mfg_init_clk_provider(struct mtk_mfg *mfg)
 	return 0;
 }
 
+static int mtk_mfg_read_nvmem(void *priv, unsigned int offset, void *val, size_t bytes)
+{
+	struct mtk_mfg *mfg = priv;
+	u32 *buf = val;
+
+	if (bytes != 4)
+		return -EINVAL;
+
+	if (!mfg->shared_mem)
+		return -ENODEV;
+
+	if (offset + bytes >= mfg->shared_mem_size)
+		return -EINVAL;
+
+	*buf = readl(mfg->shared_mem + offset);
+
+	return 0;
+}
+
+static int mtk_mfg_init_nvmem_provider(struct mtk_mfg *mfg)
+{
+	struct device *dev = &mfg->pdev->dev;
+	struct nvmem_cell_info cell = {};
+	struct nvmem_config config = {};
+	struct nvmem_device *nvdev;
+	int ret;
+
+	config.reg_read = mtk_mfg_read_nvmem;
+	config.dev = dev;
+	config.read_only = true;
+	config.priv = mfg;
+	config.size = 4;
+	config.word_size = 4;
+
+	nvdev = devm_nvmem_register(dev, &config);
+	of_node_put(config.of_node);
+	if (IS_ERR(nvdev))
+		return dev_err_probe(dev, PTR_ERR(nvdev), "Couldn't register nvmem provider\n");
+
+	cell.name = "shader-present";
+	cell.offset = GF_REG_SHADER_PRESENT;
+	cell.bytes = 4;
+	cell.np = of_get_child_by_name(dev->of_node, cell.name);
+
+	ret = nvmem_add_one_cell(nvdev, &cell);
+	/* cell.np purposefully not put as nvmem_add_one_cell does not increase refcount */
+	if (ret)
+		return dev_err_probe(dev, ret, "Couldn't add cell %s\n", cell.name);
+
+	return 0;
+}
+
 static int mtk_mfg_probe(struct platform_device *pdev)
 {
 	struct mtk_mfg *mfg;
@@ -984,6 +1037,10 @@ static int mtk_mfg_probe(struct platform_device *pdev)
 	if (ret)
 		goto err_power_off;
 
+	ret = mtk_mfg_init_nvmem_provider(mfg);
+	if (ret)
+		goto err_power_off;
+
 	ret = of_genpd_add_provider_simple(dev->of_node, &mfg->pd);
 	if (ret) {
 		dev_err_probe(dev, ret, "Failed to add pmdomain provider\n");

-- 
2.52.0