netdev - Re: [PATCH v4 08/18] net: davinci_emac: potentially get the MAC address from MTD

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Date:   Fri, 29 Jun 2018 15:35:27 -0500
From:   David Lechner <david@...hnology.com>
To:     Bartosz Golaszewski <brgl@...ev.pl>, Sekhar Nori <nsekhar@...com>,
        Kevin Hilman <khilman@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Grygorii Strashko <grygorii.strashko@...com>,
        "David S . Miller" <davem@...emloft.net>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Lukas Wunner <lukas@...ner.de>, Rob Herring <robh@...nel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Ivan Khoronzhuk <ivan.khoronzhuk@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Lunn <andrew@...n.ch>, Jonathan Corbet <corbet@....net>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-omap@...r.kernel.org, netdev@...r.kernel.org,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [PATCH v4 08/18] net: davinci_emac: potentially get the MAC
 address from MTD

On 06/29/2018 03:09 PM, David Lechner wrote:
> On 06/29/2018 04:40 AM, Bartosz Golaszewski wrote:
>> From: Bartosz Golaszewski <bgolaszewski@...libre.com>
>>
>> On da850-evm board we can read the MAC address from MTD. It's currently
>> done in the relevant board file, but we want to get rid of all the MAC
>> reading callbacks from the board file (SPI and NAND). Move the reading
>> of the MAC address from SPI to the emac driver's probe function.
>>
>> Signed-off-by: Bartosz Golaszewski <bgolaszewski@...libre.com>
>> ---
>>   drivers/net/ethernet/ti/davinci_emac.c | 20 ++++++++++++++++++--
>>   1 file changed, 18 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/ti/davinci_emac.c b/drivers/net/ethernet/ti/davinci_emac.c
>> index a1a6445b5a7e..48e6a7755811 100644
>> --- a/drivers/net/ethernet/ti/davinci_emac.c
>> +++ b/drivers/net/ethernet/ti/davinci_emac.c
>> @@ -67,7 +67,7 @@
>>   #include <linux/of_irq.h>
>>   #include <linux/of_net.h>
>>   #include <linux/mfd/syscon.h>
>> -
>> +#include <linux/mtd/mtd.h>
>>   #include <asm/irq.h>
>>   #include <asm/page.h>
>> @@ -1783,7 +1783,10 @@ static int davinci_emac_probe(struct platform_device *pdev)
>>       struct cpdma_params dma_params;
>>       struct clk *emac_clk;
>>       unsigned long emac_bus_frequency;
>> -
>> +#ifdef CONFIG_MTD
>> +    size_t mac_addr_len;
>> +    struct mtd_info *mtd;
>> +#endif /* CONFIG_MTD */
>>       /* obtain emac clock from kernel */
>>       emac_clk = devm_clk_get(&pdev->dev, NULL);
>> @@ -1815,6 +1818,19 @@ static int davinci_emac_probe(struct platform_device *pdev)
>>           goto err_free_netdev;
>>       }
>> +#ifdef CONFIG_MTD
> 
> What about the case when MTD is compiled as a module?
> 
>> +    mtd = get_mtd_device_nm("MAC-Address");
> 
> What about the case when PTR_ERR(mtd) == -EPROBE_DEFER?

To answer my own question: because get_mtd_device_nm() doesn't
ever return -EPROBE_DEFER.

I'm trying to make this work on LCDK, but the emac driver probes
before any mtd device is registered, so, I just get -ENODEV even
though I've added a partition to the device tree labeled
"MAC-Address". You can see in the kernel messages that MTD is
not probed until later.

> 
>> +    if (!IS_ERR(mtd)) {
>> +        rc = mtd_read(mtd, 0, ETH_ALEN,
>> +                  &mac_addr_len, priv->mac_addr);
>> +        if (rc == 0)
>> +            dev_info(&pdev->dev,
>> +                 "Read MAC addr from SPI Flash: %pM\n",
>> +                 priv->mac_addr);
>> +        put_mtd_device(mtd);
>> +    }
>> +#endif /* CONFIG_MTD */
>> +
>>       /* MAC addr and PHY mask , RMII enable info from platform_data */
>>       memcpy(priv->mac_addr, pdata->mac_addr, ETH_ALEN);
>>       priv->phy_id = pdata->phy_id;
>>
>