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Message-ID: <d5fa95e7-ad2a-0dc7-5c79-6a9a789dad5f@quicinc.com>
Date:   Tue, 28 Nov 2023 16:02:33 +0530
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Subject: Re: [Patch v6 10/12] pstore/ram: Add dynamic ramoops region support
 through commandline
To:     Pavan Kondeti <quic_pkondeti@quicinc.com>
CC:     <corbet@lwn.net>, <agross@kernel.org>, <andersson@kernel.org>,
        <konrad.dybcio@linaro.org>, <robh+dt@kernel.org>,
        <krzysztof.kozlowski+dt@linaro.org>, <conor+dt@kernel.org>,
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References: <1700864395-1479-1-git-send-email-quic_mojha@quicinc.com>
 <1700864395-1479-11-git-send-email-quic_mojha@quicinc.com>
 <ad38fb23-e2a2-448e-bdea-fa0985f82b50@quicinc.com>
Content-Language: en-US
From:   Mukesh Ojha <quic_mojha@quicinc.com>
In-Reply-To: <ad38fb23-e2a2-448e-bdea-fa0985f82b50@quicinc.com>
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On 11/27/2023 5:04 PM, Pavan Kondeti wrote:
> On Sat, Nov 25, 2023 at 03:49:53AM +0530, Mukesh Ojha wrote:
>> The reserved memory region for ramoops is assumed to be at a fixed
>> and known location when read from the devicetree. This may not be
>> required for something like Qualcomm's minidump which is interested
>> in knowing addresses of ramoops region but it does not put hard
>> requirement of address being fixed as most of it's SoC does not
>> support warm reset and does not use pstorefs at all instead it has
>> firmware way of collecting ramoops region if it gets to know the
>> address and register it with apss minidump table which is sitting
>> in shared memory region in DDR and firmware will have access to
>> these table during reset and collects it on crash of SoC.
>>
>> So, add the support of reserving ramoops region to be dynamically
>> allocated early during boot if it is request through command line
>> via 'dyn_ramoops_size=<size>' and fill up reserved resource structure
>> and export the structure, so that it can be read by ramoops driver.
>>
>> Signed-off-by: Mukesh Ojha <quic_mojha@quicinc.com>
>> ---
>>   Documentation/admin-guide/ramoops.rst |  7 ++++
>>   fs/pstore/Kconfig                     | 15 +++++++++
>>   fs/pstore/ram.c                       | 62 ++++++++++++++++++++++++++++++++---
>>   include/linux/pstore_ram.h            |  5 +++
>>   init/main.c                           |  2 ++
>>   5 files changed, 87 insertions(+), 4 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/ramoops.rst b/Documentation/admin-guide/ramoops.rst
>> index e9f85142182d..af737adbf079 100644
>> --- a/Documentation/admin-guide/ramoops.rst
>> +++ b/Documentation/admin-guide/ramoops.rst
>> @@ -33,6 +33,13 @@ memory are implementation defined, and won't work on many ARMs such as omaps.
>>   Setting ``mem_type=2`` attempts to treat the memory region as normal memory,
>>   which enables full cache on it. This can improve the performance.
>>   
>> +Ramoops memory region can also be allocated dynamically for a special case where
>> +there is no requirement to access the logs from pstorefs on next boot instead there
>> +is separate backend mechanism like minidump present which has awareness about the
>> +dynamic ramoops region and can recover the logs. This is enabled via command line
>> +parameter ``dyn_ramoops_size=<size>`` and should not be used in absence of
>> +separate backend which knows how to recover this dynamic region.
>> +
>>   The memory area is divided into ``record_size`` chunks (also rounded down to
>>   power of two) and each kmesg dump writes a ``record_size`` chunk of
>>   information.
>> diff --git a/fs/pstore/Kconfig b/fs/pstore/Kconfig
>> index 3acc38600cd1..e13e53d7a225 100644
>> --- a/fs/pstore/Kconfig
>> +++ b/fs/pstore/Kconfig
>> @@ -81,6 +81,21 @@ config PSTORE_RAM
>>   
>>   	  For more information, see Documentation/admin-guide/ramoops.rst.
>>   
>> +config PSTORE_DYNAMIC_RAMOOPS_REGION_RESERVATION
>> +	bool "Reserve ramoops region dynamically"
>> +	select PSTORE_RAM
>> +	help
>> +	  This enables the dynamic reservation of ramoops region for a special case
>> +	  where there is no requirement to access the logs from pstorefs on next boot
>> +	  instead there is separate backend mechanism like minidump present which has
>> +	  awareness about the dynamic ramoops region and can recover the logs. This is
>> +	  enabled via command line parameter dyn_ramoops_size=<size> and should not be
>> +	  used in absence of separate backend which knows how to recover this dynamic
>> +	  region.
>> +
>> +	  Note whenever this config is selected ramoops driver will be build statically
>> +	  into kernel.
>> +
> 
> Is there any advantage if we decouple this memory reservation from
> pstore ram so that pstore ram can still be compiled as module? Asking
> because you explicitly mentioned this limitation.

This is doable and it will be needing export(may be _NS) of
ramoops resource if ramoops needs to be build as modules.

Thanks for suggestion.
But Let's hear it from other people as well if they have something
to add otherwise, will do it next series.

> 
>>   config PSTORE_ZONE
>>   	tristate
>>   	depends on PSTORE
>> diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
>> index 88b34fdbf759..a6c0da8cfdd4 100644
>> --- a/fs/pstore/ram.c
>> +++ b/fs/pstore/ram.c
>> @@ -20,6 +20,7 @@
>>   #include <linux/compiler.h>
>>   #include <linux/of.h>
>>   #include <linux/of_address.h>
>> +#include <linux/memblock.h>
>>   #include <linux/mm.h>
>>   
>>   #include "internal.h"
>> @@ -103,6 +104,55 @@ struct ramoops_context {
>>   };
>>   
>>   static struct platform_device *dummy;
>> +static int dyn_ramoops_size;
>> +/* Location of the reserved area for the dynamic ramoops */
>> +static struct resource dyn_ramoops_res = {
>> +	.name  = "ramoops",
>> +	.start = 0,
>> +	.end   = 0,
>> +	.flags = IORESOURCE_BUSY | IORESOURCE_SYSTEM_RAM,
>> +	.desc  = IORES_DESC_NONE,
>> +};
>> +
>> +static int __init parse_dyn_ramoops_size(char *p)
>> +{
>> +	char *tmp;
>> +
>> +	dyn_ramoops_size = memparse(p, &tmp);
>> +	if (p == tmp) {
>> +		pr_err("ramoops: memory size expected\n");
>> +		return -EINVAL;
>> +	}
>> +
>> +	return 0;
>> +}
>> +early_param("dyn_ramoops_size", parse_dyn_ramoops_size);
> 
> should not this code be under
> CONFIG_PSTORE_DYNAMIC_RAMOOPS_REGION_RESERVATION?

Yeah, looks to be miss., thanks again..

> 
>> +
>> +#ifdef CONFIG_PSTORE_DYNAMIC_RAMOOPS_REGION_RESERVATION
>> +/*
>> + * setup_dynamic_ramoops() - reserves memory for dynamic ramoops
>> + *
>> + * This enable dynamic reserve memory support for ramoops through
>> + * command line.
>> + */
>> +void __init setup_dynamic_ramoops(void)
>> +{
>> +	unsigned long long ramoops_base;
>> +	unsigned long long ramoops_size;
>> +
>> +	ramoops_base = memblock_phys_alloc_range(dyn_ramoops_size, SMP_CACHE_BYTES,
>> +						 0, MEMBLOCK_ALLOC_NOLEAKTRACE);
>> +	if (!ramoops_base) {
>> +		pr_err("cannot allocate ramoops dynamic memory (size:0x%llx).\n",
>> +			ramoops_size);
>> +		return;
>> +	}
> 
> This error needs to be propagated to ramoops_register_dummy() since it
> rely on !dyn_ramoops_size . one way is to set dyn_ramoops_size to 0.

Good point, will do that..

> 
>> +
>> +	dyn_ramoops_res.start = ramoops_base;
>> +	dyn_ramoops_res.end = ramoops_base + dyn_ramoops_size - 1;
>> +	insert_resource(&iomem_resource, &dyn_ramoops_res);
>> +}
>> +#endif
>>   
>>   static int ramoops_pstore_open(struct pstore_info *psi)
>>   {
>> @@ -915,14 +965,18 @@ static void __init ramoops_register_dummy(void)
>>   
>>   	/*
>>   	 * Prepare a dummy platform data structure to carry the module
>> -	 * parameters. If mem_size isn't set, then there are no module
>> -	 * parameters, and we can skip this.
>> +	 * parameters. If mem_size isn't set, check for dynamic ramoops
>> +	 * size and use if it is set.
>>   	 */
>> -	if (!mem_size)
>> +	if (!mem_size && !dyn_ramoops_size)
>>   		return;
>>   
> 
> If mem_size and dyn_ramoops_size are set, you are taking
> dyn_ramoops_size precedence here. The comment is a bit confusing, pls
> review it once.

Ideally, both should not be set and there will always be
confusion.

Do you think, if we use mem_size a single variable both for earlier
and dynamic ramoops where based on dyn_ramoops_size=true/on a boolean
it will take dynamic ramoops path and if not mentioned it will take 
older path.

-Mukesh
> 
>> -	pr_info("using module parameters\n");
>> +	if (dyn_ramoops_size) {
>> +		mem_size = dyn_ramoops_size;
>> +		mem_address = dyn_ramoops_res.start;
>> +	}
>>   
> 
> Overall it Looks good to me. Thanks.