Re: [PATCH 3/3] nvmem: qfprom: Don't touch certain fuses

[Srinivas Kandagatla]

Hi Evan,

On 29/09/2020 21:58, Evan Green wrote:
Some fuse ranges are protected by the XPU such that the AP cannot
access them. Attempting to do so causes an SError. Use the newly
introduced per-soc compatible string to attach the set of regions
we should not access. Then tiptoe around those regions.

This is a generic feature that can be used by any nvmem provider, can 
you move this logic to nvmem core instead of having it in qfprom!


thanks,
srini

Signed-off-by: Evan Green <evgr...@chromium.org>
---

  drivers/nvmem/qfprom.c | 55 +++++++++++++++++++++++++++++++++++++++---
  1 file changed, 51 insertions(+), 4 deletions(-)

diff --git a/drivers/nvmem/qfprom.c b/drivers/nvmem/qfprom.c
index 5e9e60e2e591d..feea39ae52164 100644
--- a/drivers/nvmem/qfprom.c
+++ b/drivers/nvmem/qfprom.c
@@ -12,6 +12,7 @@
  #include <linux/mod_devicetable.h>
  #include <linux/nvmem-provider.h>
  #include <linux/platform_device.h>
+#include <linux/property.h>
  #include <linux/regulator/consumer.h>
  
  /* Blow timer clock frequency in Mhz */
@@ -51,6 +52,17 @@ struct qfprom_soc_data {
        u32 qfprom_blow_set_freq;
  };
  
+/**
+ * struct qfprom_keepout_region - registers to avoid touching.
+ *
+ * @start: The first byte offset to avoid.
+ * @end: One after the last byte offset to avoid.
+ */
+struct qfprom_keepout_region {
+       u32 start;
+       u32 end;
+};
+
  /**
   * struct qfprom_priv - structure holding qfprom attributes
   *
@@ -63,6 +75,7 @@ struct qfprom_soc_data {
   * @secclk:       Clock supply.
   * @vcc:          Regulator supply.
   * @soc_data:     Data that for things that varies from SoC to SoC.
+ * @keepout:      Fuse regions not to access, as they may cause SErrors.
   */
  struct qfprom_priv {
        void __iomem *qfpraw;
@@ -73,6 +86,7 @@ struct qfprom_priv {
        struct clk *secclk;
        struct regulator *vcc;
        const struct qfprom_soc_data *soc_data;
+       const struct qfprom_keepout_region *keepout;
  };
  
  /**
@@ -88,6 +102,12 @@ struct qfprom_touched_values {
        u32 timer_val;
  };
  
+const struct qfprom_keepout_region sc7180_qfprom[] = {
+       {.start = 0x128, .end = 0x148},
+       {.start = 0x220, .end = 0x228},
+       {} /* Sentinal where start == end. */
+};
+
  /**
   * qfprom_disable_fuse_blowing() - Undo enabling of fuse blowing.
   * @priv: Our driver data.
@@ -171,6 +191,23 @@ static int qfprom_enable_fuse_blowing(const struct 
qfprom_priv *priv,
        return ret;
  }
  
+static int qfprom_check_reg(struct qfprom_priv *priv, unsigned int reg)
+{
+       const struct qfprom_keepout_region *keepout = priv->keepout;
+
+       if (!keepout)
+               return 1;
+
+       while (keepout->start != keepout->end) {
+               if ((reg >= keepout->start) && (reg < keepout->end))
+                       return 0;
+
+               keepout++;
+       }
+
+       return 1;
+}
+
  /**
   * qfprom_efuse_reg_write() - Write to fuses.
   * @context: Our driver data.
@@ -228,8 +265,10 @@ static int qfprom_reg_write(void *context, unsigned int 
reg, void *_val,
                goto exit_enabled_fuse_blowing;
        }
  
-	for (i = 0; i < words; i++)
-               writel(value[i], priv->qfpraw + reg + (i * 4));
+       for (i = 0; i < words; i++) {
+               if (qfprom_check_reg(priv, reg + (i * 4)))
+                       writel(value[i], priv->qfpraw + reg + (i * 4));
+       }
  
  	ret = readl_relaxed_poll_timeout(
                priv->qfpconf + QFPROM_BLOW_STATUS_OFFSET,
@@ -257,8 +296,14 @@ static int qfprom_reg_read(void *context,
        if (read_raw_data && priv->qfpraw)
                base = priv->qfpraw;
  
-	while (words--)
-               *val++ = readb(base + reg + i++);
+       while (words--) {
+               if (qfprom_check_reg(priv, reg + i))
+                       *val++ = readb(base + reg + i);
+               else
+                       *val++ = 0;
+
+               i++;
+       }
  
  	return 0;
  }
@@ -299,6 +344,7 @@ static int qfprom_probe(struct platform_device *pdev)
        econfig.priv = priv;
  
  	priv->dev = dev;
+       priv->keepout = device_get_match_data(dev);
  
  	/*
         * If more than one region is provided then the OS has the ability
@@ -354,6 +400,7 @@ static int qfprom_probe(struct platform_device *pdev)
  
  static const struct of_device_id qfprom_of_match[] = {
        { .compatible = "qcom,qfprom",},
+       { .compatible = "qcom,sc7180-qfprom", .data = &sc7180_qfprom},
        {/* sentinel */},
  };
  MODULE_DEVICE_TABLE(of, qfprom_of_match);